Okay would the mystics team ability be triggered by a stunning blow attack?

By the token no not even with pushing damage but the unmodified damage part yes.

From the PAC

So, if you deal damage via Stunning Blow, yes you would take one back. Incap wouldn't trigger Mystics damage normaly, unless you crit hit. In that case, you would be dealing 1 damage (Since Incap is a 0 damage power it's subject to crit hits) and that would trigger the Mystics TA.

Just to clarify, simply DEALing damage isn't enough to trigger the TA. At least some of that damage needs to be TAKEN. (IE, the dial must be clicked.)

A key distinction.