Ummm, don't you have to have an origin for func_rotatings, if you don't want them to rotate around the center of the map? :
You can have any number of different objects rotating around the same point on a map, all using different origin brushes, and it'll work exactly the same as if it was all one entity (well, just without the face splitting, of course.) To set up your origin, just get a brush with the ORIGIN texture all over it, and place it at the point you want your func_rotating to rotate from. Tie the brush with the ORIGIN texture on it into the same entity as the other object/s, and you're good. The origin brush doesn't have to be touching anything else, as long as it's tied into the entity.