A snap roll is an accelerated stall with a one revolution spin. I believe that a "true" snap roll is done with just elevator (possibly with some rudder to control the direction of the spin).
i am flying full scale aerobatics now in a Super Decathlon and a snap roll is an accelerated stall and spin on the horizontal plane, rather than vertical like a normal spin.
the inputs for a real plane are full rudder and full aft at the same time.
i think i was going too slow cuz when i talked to my acro instructor today about it, she said i probably wasn't going fast enough.