Boot Camp really doesn't care once it makes the partition what you put on it. BUT... Unless there are a lot of good drivers for Gentoo on THIS PARTICULAR HARDWARE, you might have some real problems. The reason that there are differences in how things work on the MacBook and the MacBook Pro is that their hardware is significantly different. I would not put a lot of effort into Gentoo unless there were some pretty substantial claims of it working ON AN MBP.