In theory, as long as they keyboard in question is compliant with all the requisite ANSI/ISO standards, it should be fine. Most of the experience I have with keyboard support under the Mac OS X environment has been with USB, though I have used two different PS/2 keyboards via a PS/2<>USB adapter.
I've never owned a wireless keyboard, but I have several friends that own them and they all seem to be happy with them. Of course, they're all either Microsoft, Logitech, or Kensington keyboards, so compatibility with them is basically a no-brainer.
How well some of the more exotic keyboards out there (particularly the gamer's keyboards) work is an open question, as the only person I know who owns one (it's the one with the swappable sections) uses it on a dual-booted WinXP Pro SP2/Ubuntu 6.x box, not a Mac.