In my opinion, and worth every penny you are paying, is pure sand for leveling as any amount of compost will decompose causing the mix to settle, which defeats the purpose of leveling. After the lawn is flat, only then do I switch to top dressing as an annual touch up with a mix.
The benefit of adding compost is it can help raise the PH level and give the turf a good jump start from the nutrients it provides. For leveling a yard, it actually is a negative as it will settle as it decomposes.
I try and get the turf growing as strongly as I can right before leveling. Doing this negates any need for compost or fertilizer in the leveling stage, and the turf can push up through the sand quickly.
In summary, pure sand for leveling, a mix for top dressing, both have their place.
Edit: Keep in mind Bermuda makes plenty of compost on its own. That pure sand will become rich in nutrients in short order.