I feel that as assassin's stance says ability and not class feature, it wouldn't count. If the original post said ability and not class feature, it would.
This is clarified by the stance saying later on if you have the class feature, your SA ability is increased, which makes me feel that tje class featute and the ability to use sneak attack are seperate.
Now I Will judge the damage if it's not your only form of sneak attack, but of it is the only form of SA ,.barring a ruling from the chair, it will get a 0.