Any Server that has the MapVote "bEntryWindows=True" <-(set to True), the Window will pop up when you enter the server that will have you Set your "Hot Key" for MapVote.
Yes, a lot of servers have this turned off (set to False) but Yes, {CG}, {CMM}, {CRW} and {MHM} all have theirs set to True so you can set your MapVote Hot Key at those servers.
I also am pretty darn sure that{MHMIII} does also.

Of course you can also set it manually to an un-used key in your User.ini file, - Or, like you said, in your UT Preferences.
