I'm curious whether he intends to do a 4-speed or not. The major tactical advantage of keeping a 1:1 ratio between the omni & traction wheels is to be able to change from one to the other at full speed. There is also another (huge, IMO) build advantage to this setup which should help answer the actuation question, and it is outlined on slide 3 of this paper:
http://www.chiefdelphi.com/media/papers/2968
I think I need more detail on how the drive train will be run before commenting further. For example, do you plan to use 1 serpentine belt or two belts per side?