Ninjutsu damage does NOT wake up a sleeping character, so you can put a character with a Ninjutsu-only type standard attack in front of or behind a Fire main.

Always happy to provide info :P. Nothing more annoying than having Tobi and Fire main in the same row. Permanent sleep and ignition ;P. Tayuya, unfortunately, isn't that good though...I don't know why the Sound Four don't have their curse seal upgraded forms.

I'm not sure what you mean by "probably not 100% true" and you listed Tobi as the example, when Tobi is the one I listed that would work with Fire main's sleep...I don't need to just try it, as it is my MAIN lineup and the only time they wake up, is when Tobi initiates a combo (which one of my characters will inflict Taijutsu damage) or if they were slept BEFORE their turn, they will wake up NEXT turn (my main is in position 3 so if I have higher initiation than their position 3 or I sleep a position 4, they will unable to do their standard attack this turn, but will wake up at the start of next turn).

Another note, is that Ninjutsu-only Mystery skills also don't wake up sleeping characters. You can try this with Fire main's mystery.