UC introduced Style feats to salvage the poor Monk. I will cover the ones of possible use under "Style feats." Most are based around melee and unarmed attacks and will thus be of no or limited use for the ZAM. You can only use one style feat tree at a time unless you forgo flurry of blows to be a Master of Many Styles (do NOT do this!), so pick the one you like the best, if any appeal at all.
Clustered Shots: If UC is allowed, you need to get this feat. DR becomes a non-issue, instantly! See Deadly Aim on why you may be able to grab this as your 7th level feat. The argument is more compelling here, since you can only ever use Clustered Shots on a full attack, and you always have full BAB when you full attack.
Deathless Initiate: Just mentioning because it lets you full attack when you otherwise could not, and any ZAM going for Horizon Walker will need Endurance anyway. Only relevant to Half-Orc Unbreakable Fighter / ZAM / Horizon Walkers, a pretty narrow group, and not that great even then.
Deathless Master: Even if you want Deathless Initiate, this follow-on feat is just terribad.
"Dimensional" feats: These are meant for melee monks to get in a full attack, and suck for them, too (best on a Magus, Eldritch Knight, or melee Horizon Walker). Ignore them.
Enfilading Fire: If you've got an ally to take this with...it still sucks. Requires another teamwork feat, only gives you +2 attack, and does nothnig for your friend. Awful.
False Opening: Too much risk for too little payoff. Perhaps as a dedicated build w/ Snake Style feat tree and some sneak attack through multiclassing, but I doubt it'd be worth it even then.
Guided Hand: This is how the cleric makes you feel obsolete. GRRRRR!!! Just wait, the book's not done handing off your class features just yet...
Hammer the Gap: The bonus damage is awfully low, but you'll get some every round you shoot at things with sizeable hp. A "if nothnig else seems good at this level up" option.
Impact Critical Shot: Bows have an awful threat range and the chances of getting a nat 20 (or 19 w/ keen/imp. crit) and then also rolling really well on the confirmation is...low. Don't expect to bull rush anyone very far, should probably just use the prone option. Oh, and a lot of times your crit will probably kill the foe anyway. I'd hold out for ZAM 17 to use Punishing Kick on my arrows instead if possible, over this.
Landing Roll: I was going to say this is nice in concert w/ Ki Stand for those hyper paranoid of falling prone. But then noticed it costs an immediate (ie, no swift next turn) to use. Ho hum...
Opening Volley: You are not a switch hitter and this is utterly pointless past level 2.
Snap Shot: This is where we get angry. Holy theft, Batman! Fighter gets your Reflexive Shot, gets it EARLIER, and (see below) can do it better than you! WT-EVERLOVING-F?!
Snap Shot, Improved: If your DM allows you to sub. flurry and Reflexive Shot for Rapid Shot, BAB +9 (you get Reflexive Shot at 9th...), and Snap Shot, consider going for it. You'll basically have a 15 ft threatened area. If he does not, yell and scream at him for letting Joe Fighter do your own mid-level class features better than you can. :(
Snap Shot, Greater: Your lower BAB really hurts with qualifying and benefiting here, even if your DM is nice and houserules in your favor. That said, the benefit here is pretty pathetic, so not much loss. Fluff text mentions a threatened range increase, guess it was changed at some point to suck.
Target of Opportunity: If you have a party large enough to support two archers, you both may want to get this teamwork feat so each of you get one extra attack every round.
Style Feats
Crane Style: You can fight defensively with ranged attacks! I seriously did not realize this. As an archer, you shouldn't be getting melee attacked that much, but this is still a very appealing style tree. Base style feat, not so much. Even when accosted by melee, not sure a -2 to hit for +4 AC is worth it.
Crane Wing: Now it's worth taking the -2. Savor the look of sadness on your foe when his charge attack auto misses!
Crane Riposte: Still decent, but hardly necessary.
Dragon Style: Decent mobility options, works well with Parting Shot. If you're still using unarmed strikes to threaten with, you get a small damage boost on your first AoO each round.
Dragon Ferocity: Ignore the unarmed damage bonus. This is handy because you get the shaken effect from ANY attack that crits or Stunning Fist (Ki Focus Bow, recall). Can't take it till you have Stunning Fist at level 11, though.
Dragon Roar: Worthless.
Mantis Style: Once you get Stunning Fist, this is basically Ability Focus with a freebie +1 use per day for the low, low cost of 3 ranks in Heal.
Mantis Wisdom: This is useless to non-traditional monks..
Mantis Torment: This is incredibly bad. Even for a traditional monk.
Marid Style: Awful. The only reason to consider this is...
Marid Spirit: To add a nice Entangled effect (they get a Fort save to negate, though) to your Elemental Fist bow shots. No idea why you spent 3 feats just to entangle people at level 17+, though.
Marid Coldsnap: Your normal flurry is superior.
Monkey Style: No extra feats needed, buffs acrobatics checks, and with a fairly easy DC 20 check you can stand from prone as a swift w/o AoOs, making this much better than Ki Stand.
Monkey Moves: Not sure how useful the mobility options for climbing and crawling are by now, but it could certainly prove useful.
Monkey Shine: Maybe on a Combat Reflexes build, but I'm skeptical it's worth the feat.
Shaitan Style: Awful. The only reason to consider this is...
Shaitan Skin: To add a nice Staggered effect (they get a Reflex save to negate, though) to your Elemental Fist bow shots. No idea why you spent 3 feats just to stagger people for 1 round at level 17+, though.
Shaitan Earthblast: Your normal flurry is superior.
Snake Style: It will be hard to optimize Sense Motive enough to make this relevant, and relying on it often prevents use of the ki pool for more attacks.
Snake Sidewind: +4 to avoid going prone is the only useful thing here, I'd go with Ki Stand or Monkey Style rather than this.
Snake Fang: Even as an archer, this is pretty swanky for an AoO build. Not sure it's worth the pre-reqs, though.