Matthew I do not doubt your idea.
I fully agree that both photos might be from the VRC, and I certainly believe the bottom photo is VRC without much doubt after talking to you. However, if you are correct, if the top photo shows a regular regulation uniform as you suspect, it certainly opens up the strong possibility he is not VRC but from a regular regiment.
I just wanted to bring the top photo into more of the discussion now to learn what else might be discovered about it. Asking for more ideas does not mean your suggestion isn't given real weight especially since you were dead on in your appraisal of the bottom photo.
All we really know is that these photos come from the same family album. And that the family was from Iowa during the war. It is possible both men began their service in the same regiment and then both later went to the VRC. The family did have relatives back east in New york I believe so it is possible one or both might also be from other states than Iowa.
The bottom photo leaves little doubt he is VRC, and I certainly thank you for helping make it even more certain.
An expert in reproduction uniforms also has little doubt the man in the lower photo is wearing a VRC uniform. And a third opinion agreeing fully on the VRC uniform came from a Park Service Librarian at a Civil War battlefield.
So far none of the names known in the family have turned up on a VRC roster but we are still looking. At least it narrows the search down to something tangible. If two family names are found in the VRC rosters that might cinch it for both like you suggest Matthew. If we confirm it, especially for the top photo you'll be the first to hear about it.