Great question. How is he on Buzz Lightyear's Astro Blasters? Roger Rabbit doesn't have to spin much--in fact, if you don't spin the wheel, I wouldn't personally really consider it a spinny ride at all, though the cars will rotate some even if you don't turn the wheel.
If I recall correctly, Mr. Toad is like a regular dark ride like Snow White, but perhaps with more sudden turns. You could probably look at a ride-through on YouTube to try to discern if it would be a problem, but if he has no problem with the dark rides in WDW I can't imagine Mr. Toad would be a problem.