To our knowledge, only one hotel on the Strip has a pool: the Tropicana. The Trop was joined in recent years by an off-Strip non-gaming property -- the Platinum -- which also has an indoor facililty. They're both indoor-outdoor pools that can be closed to the cold in the winter. The former's heated to 60 degrees and the latter to 76 degrees.
However, there are other options, depending on your requirements. While in days gone by pretty much all the hotels closed all their pools in the winter months, these days it's the norm to keep at least one heated pool open year-round and, luckily for you, we keep just such a list, including what temperature they're heated to, where we can get it. Just check out the Pools section in the LVA Visitor Guide for this and all manner of other useful information.
One thing to bear in mind is that, outside of the summer pool party season, when a bunch of really Cool Pools are open to the general public (albeit often for a fee and with a dress/undress code), there's one other option, aside from the public pools, if you really need to submerge yourself. For a fee, the spas at the J W Marriott, Tropicana, Ritz-Carlton, Trump International, and Las Vegas Hilton all have swimming pools that guests of the spa may use.
