Yep - my experience has been that any loose fitting shirt meant to be worn untucked is just fine as long as it is long enough, or your holster rides high enough. I always wear a T-Shirt, even when open carrying with my outer shirt tucked behind the gun just in case I decide to flip my outer shirt over the gun. I don't like the feeling of bare firearm against my bare skin.
That's the only different for me between open carry and concealed carry - the shirt either gets tucked behind the gun, or over the gun.