Hawks fan here (don't shoot!). Tarasenko looked really bad coming up after that hit. Eyes were rolled back in his head, and his jaw looked possibly broken. He did not look good at all. I would be bummed if he was out for any length of time, I love watching the kid play, even if he is a Blue. I was rooting for him to win the Calder.
Watch the replay again. He clearly hit him with his arm.
I won't debate if it was dirty or not because the angle is from the wrong way but his arm was tucked in in front of his chest not sticking out so it certainly wasn't an elbow or something even if his arm was the point of contact.