Rotation has been in the quake engines since quake 2. Now, assuming they haven't taken it out (I'm at work, can't check Radiant) here's how you do it- Create the brush you want to rotate, or multiple brushes.
Then create an axis brush at the center of rotation, then load up the common textures and use the ORIGIN shader (again, I'm assuming JK2 kept these the same, if I'm wrong then someone please correct me) on the brush. This brush is what your platform will rotate around- it won't show in-game. Now select all the brushes you want to rotate, as well as the origin brush. Right click, go through the entity list and make the group of brushes into a func_rotating entity. The comments in the entity editor for func_rotating should help as well.
Again, I could be completely wrong, but most of the quake engine games since quake 2 don't seem to have deleted the func_rotating entity, so I'm assuming JK2 still has it. I would venture to guess that you can use switches in mp as well.