How does True Sight interact with this type of creature?
If you click the link provided above, the other thread has your answer. Right in the spell description for True Seeing, it states that it does not pierce concealment.
What if the creature is using the hide skill in addition to being concealed?
This is the tricky area where it's pretty much up to DM interpretation.
Total Concealment = can't be seen, ergo, you don't really need to hide.
A reasonable way of running it in game would be to treat the total concealment as a 50% miss chance, as well as an improved form of Hide in Plain Sight*, allowing the creature to make a free Hide check each round with no penalty, and if the opponents fail their spot checks, then they can't see the Shadow Creature. I'm thinking of running it this way in the future; Shadow Creatures are going to start being a major faction that my PC's will have to go up against.
*Note that the Dark Creature template, which is supposed to be a toned-down and streamlined version of the Shadow Creature template (at +1 LA instead of +2), gives HiPS, as well as a racial bonus to Hide and Move Silently checks. The greater version of the template only gives a bonus to Move Silently checks. That dichotomy reinforces the straight RAW answer, in that Total Concealment = can't be spotted. Shadow Creature doesn't give a racial bonus to Hide checks, because most of the time the Shadow Creature doesn't even have to make them.
That said, there's nothing preventing the shadow creature from using the Hide skill while shadow blended. The shadow blend even gives him the concealment that allows the Hide check.