An insole will steal from your deadlifts by creating an imbalance in your stance - namely, it will introduce instability or give under your foot. This is bad, it's a spot that power will literally leak out through. If there's some way you could create a rigid insole with no give, maybe.
I will tell you that I also have extreme supination in my gait, i.e. I walk like a duck on the outside of my feet and I have no issues related to that from deadlifting.
I'd personally say no on the insole unless it was very rigid or built right into the shoe.