Would you consider Xcode and Poser 6 powerful tools for game making?

yes
its how you use them that matter though

Can poser produce low poly models? My experience with it is that it exports a stick figure maneguin at like 6,700 poly's. Not sure if they have given the ability to cut the poly count but maintain some level of detail. If you are going to make sprites based games, Poser works like a charm.

Yes I think you can lessen the quality of graphics but not sure how to work with it perfectly