Hello WEDWDW. Yes, re-entry into the water parks is perfectly acceptable. Be sure to bring your pass with you when you return and get a hand stamp on the way out of the park when you leave for a break.
The one thing you will not be able to do is visit, say, Blizzard Beach in the morning and then 'return' to Typhoon Lagoon later that day. That will require two separate 'Plus' options.