Hello Dan,
Yes, VE PRO 6 licenses will UPGRADE your VE PRO 5 license, so you can use either VE PRO 5 OR VE PRO 6.
VE PRO 6 will overwrite VE PRO 5 on your computer, so you have to decide which version you want to use.
Also, VE PRO 6 projects will NOT open with VE PRO 5 (only the other way around).
It might be a good idea to stay with VE PRO 5, if you need RTAS to be available.
Rolling back to VE PRO 5 is not hard (simply use the UNINSTALLER, then install VE PRO 5), but might lead to confusion when you´re going back and forth.
Best,
Paul