Man I love Sunn hemp. I think it will do great.
I think I’ve gotten so into this regenerative ag thing I like to plant plants of different types (grass, legume, etc). But there is nothing wrong with planting those two together.
The two I see mentioned the most are to plant with alyceclover and/or cowpeas.
I would go a touch higher with sun hemp if was me. Up to 5lbs/acre. You don’t want to crowd out the deer vetch, but I like having enough of the other you know it is there. Im doing 3 and 2 pounds of the sorghum and sunflowers with my deer vetch/Alyce clover.