Actually no, this is not entirely correct. The Pariahs' Bane Expansion was designed to be 100% compatible with multiplayer.
Unfortunately we didn't have enough time and opportunity to thoroughly test it to make sure everything in multiplayer works correctly, the same was as in singleplayer, but all quests and everything else was designed to work in multiplayer.
So, feel free to give it a try. But as ai_enabled said, the players will need to have the expansion in order to connect to that server.