Will the fitting be different if I ride on the hoods as opposed to riding with my hands on the drops? If I get fitted will I be comfortable on only one of these two riding positions?

Bonus video:
https://www.youtube.com/watch?v=w8yC_MKBPyA

No. A drop bar is designed to be used for several positions. Your body would not tolerate miles of riding in a single position, which is why distance and performance oriented road riders choose some variant of a drop bar.

Most riders get fit with their hands over the hoods because that is their most neutral position and where they do most of their riding.

Thank you oldbobcat.