Neither my past nor present teams have used the AM Traction Wheels, but I can provide a bit of insight.
Pretty much every wheel sold with the intention of going on an FRC robot will have the same 1.875" bolt circle you see in the kit wheels. I believe that between AndyMark and IFI, the only oddball is the AndyMark Trick Wheel (which you probably should be skipping over if you're looking for omniwheels anyway, as AndyMark has since released other models with many improvements).
Last season, the Capitals took a different route and chose to skin the kit wheels and add on the tread that is used on the AM Traction (and AM Performance, and IFI) wheels. We took the wheels to the bandsaw and cut away the gray tread; you can see the result
here. From there, we riveted on incline conveyor belting (search mcmaster.com) cut to fit the wheels. Finished diameter was about 5.5", and for far less than buying other wheels. While I don't generally enjoy taking business from AndyMark--they're good people who make good product--the cost savings are hard for us to pass, especially with the improvements to the 2008 kit wheels. (For reference, the 2007 wheels held up fine for us; after Palmetto, BE, and a few demos, we're just now almost to the point of needing to replace some tread.)