Actually the Ocean should be warmer in December then it is in July!
I am a So Cal girl so I will swim almost anytime in the ocean but am a bit pickier about the pool now that I have one myself.
If its warm enough, does depend on where you are from firsth and then the weather. April can be a tricky month with it possibly being from 50-85 degrees just depending. The good thing is like they said the pools are heated so you should be fine most days, unless we get a freak coldspell.
We stayed at the Knox hotel last June and the pool wasn't - it was too cold for me, not for my daughter though. It was very breezy and that didn't help at all.
I'm sure my kids will swim when we are at the Crowne Plaza next month. LOL And then at the HoJo if we make the time for it. They wanted to swim in January...when it was raining! LOL We are from Nor Cal, they would swim everyday if we had a pool. LOL I may not swim but I know the kids will. In October of 07 we stayed at the Trop and the kids swam while I sat at the pool in my jeans. LOL