Offline
Hill has the effect of slowing down the defense because they have to account for him on every down.I think it's less relying on him and just the nature of Taysom as a weapon and what he brings to the offense. You can go 21 or 12 personnel and the defense still has to match up like it's 11. He plays multiple distinctive roles on offense. He is strong blocker at the POA and is dynamic with the ball in his hands. He has the size and speed to present matchup issues out wide.
Oh... and he can throw the ball as well as a starting QB.
Just having him on the field gives the offense some juice, and he is a great situational weapon (3rd down, short yardage, red zone). That's in large part why the offense is so productive with him out there.
All that to say it's not that Kubiak is "relying" on him in terms of changing the scheme or even the way he calls plays with Taysom out there. It's more the natural stress it puts on the defense with his presence.