No pool hopping per the rules. Every resort guest is permitted to swim at their own resort but hopping is not allowed. In the rare instances a resort pool may be down for service, guests of that resort are given an designated alternate location to swim in nearby.
Also per the rules, resort guests are free to enjoy the other resorts but that does not extend to pool privileges.
Of course, if these are brand new rules that a CM gave you, we will hear more of it but for years the "No Hopping" policy has been in place. Also, CM's have been known to give incorrect answers to asked questions. Bus drivers are famous for this...
DVC members, as a DVC benefit, can pool hop I believe between DVC resorts. That's been the extent of it.
Bama Ed
PS - there is a boat between the Contemporary and the Fort too but that doesn't make them "sister resorts".