The Frostmoon Pack is the only remaining werewolf pack on Solstheim. All other werewolves on the island are loners. Another pack was said to exist but it was wiped out by werebears. Hjordis' dialogue reveals that this was her original pack.
If the Dragonborn is not a werewolf, they will behave as if he/she is trespassing and turn hostile after a while. If the Dragonborn leaves before they turn hostile, becomes a werewolf and returns, they may still become hostile. The use of high level calm spells may be required to trade with them if such is the case.