That's AWESOME.
<Tech Inspector Mode>
Just a few things to consider before finalizing your design... are those tires rated for 4,000 RPM, or whatever it is that you are running them at?
An 8" wheel at 4,000RPM would travel... let's see... 0.2m x 3.14 x 4000 / 60 = 42 m/s? That's 150 km/hr. I don't think many dolly carts are rated for freeway speeds!
And you can calculate the "g" forces acting on the tire pretty easily too...
No doubt you'll be building shrouds for the wheels as part of your design, but do a good job of it. If the frisbee, travelling at one half the edge velocity of your shooter wheel travels 50 feet, how far would a chunk of tire travelling twice as fast.
Or, for that matter how far would a
chunk of thumb?
I don't want to take away from the fact that that is one heck of an amazing shooter, and I think it is awesome that you posted the video, and I know you've probably got some safety plans in the works already... but
I also want teams to know that if they showed up with that shooter in that configuration that they would very like fail tech inspection. 
Jason </tech inspector mode>