I haven't needed to configure X on OpenBSD at least five years now. The X server does that automatically, just like on Linux. For the record, I haven't needed to on FreeBSD either, but I've run that much more sporadically, so take that with a grain of salt.

My impression was that Xorg has obviated the need for manual configuration in all but the most extreme cases. Multiple monitors are easy with xrandr, but I'm not sure how multiple graphics cards will work.