A few we've looked up seem to close, but the weather still looks good. We are planning a trip there for the week after labor day. Thanks!
Certainly some of the hotels keep their outdoor pools open after Labor Day. Labor Day weekend may signal the end of summer, but that doesn't mean that the weather isn't still good. If it is hot and steamy (which it is... deep into the fall), many hotel pools will remain open well into the fall season for many hotels.
If you have any concerns and to be certain, please check with the specific hotel that you are interested in before making your reservation.