Visiting the pools at other hotels is called "pool hopping' in Disney lingo and, for the most part, it is not allowed. Guests at other WDW resort hotels are almost never allowed to hop to the pool at the
Beach Club (they make periodic resort ID checks). The Beach Club pool, called Stormalong Bay, is so fabulous that if everyone on property were allowed to go there, then the actual resorts guests would never get to swim.
There are a few times when pool hopping is OK. First, if your own hotel's pool is undergoing repair or refurbishment, then you will be given pool rights at another hotel. Also, members of the
Disney Vacation Club (DVC) are allowed to pool hop during non-peak times of the year, but not to the Beach Club or Animal Kingdom Lodge. Guests of the two sides of the Port Orleans resort (French Quarter and Riverside) can use the pools at the other. And guests of the All Star hotels may use the other All Star pools. (But this does not include Pop Century.)