You can cancel some Specialmoves like Kabal´s "Dash" or Sonya´s "Military Stance" with a special input (e.g. b+BLOCK, or bb/ff).
Afaik Smoke doesn´t have cancels in that regard.
Normally when you talk about cancel, you mean canceling from one move into another.
You cancel the recovery frames from your move into a special move. In Smoke´s case you could do 1/2/3/4 and cancel into SmokeBomb.
1~SmokeBomb etc..
or 11~SmokeBomb. So yes, you can use cancels in Combos.
The speed for your cancel varies on the move you are using to cancel from; plus you can´t cancel from every move.