I'd really recommend using the magic item compendium and spell compendium, with a few exceptions they're quite well balanced books... when compared to other books in 3.5 at least.
The other thing would be to allow Wilding Clasps from... ugh either MotW or Magic Item Compendium or both... long story short though they're 4,000gp and can attach to weapon / armour / worn item and allow the item to be used whilst in wildshape.
I mean if those two options were there the Druid would have access to wilding clasps and a range of spells which would leave him with nothing to complain about compared to a swordsage or blackguard.
Obviously the Blackguard is homebrew but I assume it's about the same strength as a Paladin. The Swordsage is a tier 3, the Paladin is a tier 5. Now if you've buffed the Blackguard a bit with homebrew maaaybe it'd get to tier 3. (unless you're using Cleric as a base but you didn't mention it so I'll assume no higher than tier 3.)
So you've got two tier 3 melee fighters and a slightly nerfed Druid. The Druid has shapechange for laying down a reasonable beatdown in melee, if he had access to bite of the X and buffs like that calling him tier 3 for shapechange melee wouldn't be out of the question in my opinion... versitile because he can adapt to forms with flight, swim or burrow if needed. On top of that the Druid gets a pet which is just as good as the Tier 4 Ranger's pet. Then we get to the spellcasting.
You've limited the spell selection a little, as opposed to "every druid spell ever written" which is the case for RAW Druids, limiting the books allowed limits the spells known of course. Whilst limiting this isn't unreasonable and doesn't really effect the spell casting capability of the Druid.
Spontaneously casting ANY spell he knows however is amazing... just making him a powerhouse magically. I mean compare this to the Sorc and Wiz
Wizard T1 - knows a similar amount of spells (ie. LOTS) but has to prepare them.
Sorceror T2 - knows a small selection of spells (ie. like 4/5 per CL without cheese) but can spontanously cast them.
Druid also has the same spell amounts per day as the wizard, so less castings per day than a sorc, but spontaneous from a much bigger list
The sheer flexibility makes this spellcasting Tier 1 or at least 1.5 imo, it's outright stronger than wizards T1 casting, but Druid's divine spells are in my opinion a little weaker... but that just depends on selection I guess.
So is your (T1 caster, T3 melee, T4 pet) Druid weaker than your T3 fighters? Nope... might he shapechange without wilding clasp and get save or died or destroyed? Possibly without the compendiums.
Is he viable? I would worry more about the blackguard.
At least that's how I see it.