Are the Zuma a metaphor, satire, do they reflect some aspect of humanity, are they antagonists to the player characters, or what? I don't know anything about them, and whenever they're discussed no one actually bothers to discuss them directly. So... what are they?
I had the same problem when I joined Dwilight and realized they weren't a normal realm. They are a GM controlled Daimon realm who (from most accounts) are fairly benign compared to their Beluterra counterparts. As far as I can tell, they are the boogymen 'other'. The intentionally abstract and mysterious mythical creatures sent to frustrate humanity.
http://wiki.battlemaster.org/wiki/Zuma