I'm not sure it's truly possible to venerate the entirety of the Red Pantheon - in all its past instances, it's never been a true 'pantheon' of gods, but a varied lot of entities with their own spheres of influence, goals, etc. Their numbers are beyond counting and they don't have a rigid hierarchy. A tribe worshiping a red god on one side of the world may be totally oblivious to those on the other side.

Not all red gods are even aware of others of their kind, or if they are, don't pay each other much heed. In fact, it's been common for them to fight amongst themselves just as often, or more, as they work together. It's a catch-all term, really. A leviathan might set itself up as a red god of a mer people, but that'd be totally unrelated to some kind of manticore dominating a mountain tribe in a different part of the globe.

That said, in a place like the Red Desert where multiple red gods have gathered, due to the abundance of mortals to ensnare and affairs to meddle in, there might be more interaction and people taking several patrons as a result.