Inside Mac Games says:
"As of yet, we still have no concrete confirmation regarding a Mac port of either Unreal II or Unreal Tournament 2003, though several Mac publishing and porting houses have expressed more than a passing interest in the project. IMG will be sure to inform readers as soon as we hear any word on this one."
This was as of 6/25. I'm positive someone will do it, but it hasn't been decided yet.