In RQG, it is explicitly permitted to be an initiate of multiple cults. Keep track of Rune points separately, remember that means you have two temple hierarchies to keep happy, etc. But you can do – the rules say that explicitly.
In the forthcoming version of the rules, that’s the same as well. As the rules say:
Initiation in Multiple Cults
It is possible to be initiated into more than one cult. You must pass the appropriate tests, and this always requires that the cults be friendly or associated. You must also obey the commands of the priests of each temple, participate in the cult holy days of each cult, and perform properly and completely all duties and responsibilities to each temple.
You must maintain a separate pool of Rune points for each cult you are a member of.
In several nonhuman species there is a near universal cult – think Kyger Litor or Aldrya that almost every member of that species initiates to. Then there are some additional cults that are layered on top – Argan Argar, Xiola Umbar, Yelmalio, Zorak Zoran, etc. Pretty much every troll is an initiate of Kyger Litor, and a large percentage worship someone else on top of that.
Human societies often have a couple of predominant deities – think Orlanth/Ernalda – but they don’t define their societies as much as Aldrya or Kyger Litor define elf or troll society. A few people do initiate into multiple cults, but in the society as a whole, it’s usually a rounding error.
Adventurers can be different, and in many campaigns they are. Personally, I usually advise my players against it though, as I think little is actually gained. But then again, I tend to view that as pretty much the same thing as multi-classing, which I usually viewed as a tedious munchkinism. To each their own.
