I use him at G8 against the rancor. Team is Teebo, QGJ, Tusken Raider, Phasma, and Dengar. Did 2.6 million in my last raid (solo P1, about 30-40% into P2).
Dengar's damage is abysmal, at least at G8. Mine is a "death by a thousand cuts" team. His basic will provide assists though, and since I have 3 tm removers he has a 3/4 chance of calling one of them which can help a lot at times. His primary selling point is his tenacity down, but his speed down can occasionally be used if Phasma whiffs on hers.
He is an inconsistent factor though. His speed down has a low proc chance and is unreliable (lasts for 3 turns if it does land though, plus can stun to handle side pigs), and even with crit chance mods his tenacity down has low chance to hit. Phasma adds consistency with guaranteed crits and speed down.
Kinda rambling about him at this point but I hope it helps @OP