Yes, you need reservations for Burn the Floor, Million Dollar Quartet and some comedy shows in Headliners. I think you sign up in Headliners when you embark. On the Joy in September we did not need reservations for Broadway Unplugged but it may be different on the Getaway.
By the way, we were just on the Enchanted Princess in November for a 14 day cruise. We really liked having live shows in the theater every night but some of them were pretty lame. The production shows were good but most of the one-time guest entertainers were terrible.
I'm on a short, 5 day Getaway cruise Feb. 1st and was trying to figure out how to manage seeing all the entertainment. Looks like there may not be enough even for us.