There are competing modules for one and the same type of hardware, the "official" wavelan drivers and the ones Jean Tourrilhes and likeminded folks have developed for Orinoco cards, for example. Check the
whole entertaining story, then come back.
Done?
Ok.

The USE flag in Gentoo, most likely, permits you to make a choice about support for drivers compiled into other software, like, I don't know, maybe all those radio signal strength sniffers like Kismet etc. I don't expect it to have anything to do with the modules themselves, you still need to build those, either into the kernel or externally from something like the Wireless Tools (emerge wireless-tools).
I suggest you go back to Jean Tourrilhes' pages for anything you want to know about wireless LAN cards and Linux. If it's
not there, you can be almost sure it's nowhere to be found.