_ or the Poser characters, and I can't seem to find the license for their commercial use._

The general rule is that you cannot use a 3D model in a commercial (or even free) 3D game unless you either have a commercial gaming license or the creator/rights owner specifically states that you are allowed to do so.

Let me put it this way, if you use someone else's mesh in your game (commercial or free), it is essentially like using a several-minute long clip of a copyrighted TV show, news video, or movie in your video/movie/documentary, even if it is a non-profit project. You would need a commercial license to use their video (fair use rules are far more lenient towards educational facilities and students)