Well I’ve been here since 1998 and I don’t recall there ever being any kind of rule or even a concern that one is a member of other sites. I would guess many here are activist that post to many sites. The only issue I can think of being a member of another site is if it were a skinhead site or the like.
There are some “anti-Freeper” websites on the net. If someone was bashing Free Republic at one of these other sites it could get them zotted.