when I called and asked about this option I was told you get as many days at wet n wild as you bought Universal tickets...in other words 3 day park = 3 days wet n wild, 4 days park = 4 days wet n wild
another options you might consider is
http://www.undercovertourist.com/orlando/attractions/universal-studios-florida.html#tickets
Universal 3-Day Base Ticket Plus Wet n' Wild $143.95 (includes tax and free shipping)
Admission to one of the following theme parks for each day of the ticket - 3 Days (1 park per day; no "Park to Park" access):
Universal Studios Florida®
Islands of Adventure®
plus you have 3 admissions at:
Wet 'n Wild® Orlando
it's spelled out in black and white