Yes, let me clarify a bit: everyone uses personas to one extent or another, here and everywhere. Some use them more strongly, especially online, to be wittier, or more forthright, or what have you; and some use them more strongly still, going a step further and having furry or vampiric personas, for instance.
I can see that if you yourself aren't all that different here, it can be disconcerting to see a string of cat people curling up in laps and conversing mainly by purring; but in some cases, at least, I don't believe it's a deliberate put-on, but rather a long-standing habit.
If there is any such division between a light RP shoutbox and a more general shoutbox aimed at socializing, though, the idea would be that anyone who prefers to more obviously role play (whether that involves being a cat, a vampire, or a barbarian warrior) should do the bulk of it in the appropriate area. There wouldn't be a sign out front saying "No furries allowed!"; just a request that if you primarily want to act out sparring matches between werewolves or other off the cuff roleplaying scenarios, that you do that elsewhere. An occasional mention of having cat ears or a fluffy tail in the socializing area wouldn't be something we would have the time or urge to police very strongly, I imagine.
Purely on a personal level, I'd rather not have any shoutbox divisions at all, but then, I don't use the existing one much. :)