Game industry veteran here...
It's an interesting idea, but there's a some problems. First, the crossover between those who need art in their spare time, and those who know how to contribute to projects like Blender.
In reality, the people (like me), who love making games and are constantly on the lookout for artists to help out with side projects, spend all of our time doing gameplay code. Heavy 3d math, number crunching, data management -- that kind of stuff tends to fall under the category of things we don't like doing -- thus the expertise and passion for making games themselves.
On the flip side, the programmers with the ability to contribute to a project like blender, are the kind of programmers who are specialists in a particular field, and thus, from my experience, don't really branch out from that in to the kind of things that would need art on the side.
Granted, these are generalities, but I've been in the industry for eleven years and I've only met one person who crossed those boundaries (one Stan Melax, a dude smart enough to correct John Carmack and passionate enough to walk away from a job when it doesn't challenge or interest him).
Second, those of us who are passionate about making games and do need art, are often more interested in collaborations which further our side projects. If I were to contribute to blender, this doesn't really get my own projects further. At least, not in a parallel fashion, more it's like I'm doing the coding AND the art. Only I'm trading unrelated coding for art. Really, game programmers who do this stuff on their own time are often selfish and/or extremely focused on our own projects.
Third, even if I did contribute to blender as a trade, the reality is that it doesn't further my skills in the direction I actually need for the stuff I do. So ultimately, the whole thing is kind of more downside than upside.
Anyway, not to say it's not an interesting idea, and that it won't rope in a few people, but it's going to be hard to find those people, ultimately.
