When conducting an ASU inspection, should you be able to see the brass ranks on the soldier's white shirt if worn underneath the jacket?

All depends on the size of the uniform, how it's tailored and the size of the Soldier. Some times you can, other times you can't. As long as they are placed in the correct spot with the correct measurements, then it's all gravy.

There is nothing about that in the regulation. As long as the collar rank is measured correctly it is fine. Really, depending on the build of the soldier it is just going to happen.