Well, there’s The Wolf Cult. Frequent RP in Duskwood, rituals and initiations, spreading the worgen curse, etc. Not much in the way of undead or elves, but a Deathknight worgen has joined us recently, and playing a Kaldorei-Worgen is possible as well.
I’m trying to think of other cult guilds around. I know there are… or at least were a few, but I’ve found a lot of small guilds don’t post on the forums. Roleplaying in Duskwood so frequently, I’ve also seen a guild that frequents Darkshire (Malum Discordiae) but I know next to nothing about them.
I’ve been looking for new members for Xorothian. We are a warlock only guild. The RP is sort of remnant of the burning legion. We accept any race as long as you’re a horde side warlock. But the concept for the guild I was considering was very cult like.
In terms of being active, we are new. I really only have 1 officer at the moment besides myself. And the few we’ve recruited are not on very often so I surmise they are someones alts. But I’m on most nights.
You can also look at the Sunfury Battalion. They are a belf only guild though I am unsure about the cult part. They might be of interest to you though. https://us.forums.blizzard.com/en/wow/t/sunfury-battalion-recruiting/308731