I have started a lets play on my channel for hexxit. But Hostile mobs from mods nearly never spawn... When it is night. I haven't seen one mob that isn't in vanilla. Passive mobs spawn more, but not as much as I want them too. And, custom mob spawners wont work.. They dont spawn mobs whatsoever (Walker Dungeons, Pirate Ships), I am on normal difficulty and havent changed any config files.
Picture of Spawner: http://i.imgur.com/7wC6aXU.png