I don't see a reason as to why a Staff member shouldn't join a group to rp.
People, as said, fear that if they cuss something and you see it in the group you're in, they will get kicked or banned.
But, you too know how groups work and that there is bad language in 90% of the cases. So I'm sure you won't really do anything about it and maybe even join in?
There's nothing wrong with having a Staff member in a rp. Some people don't even know who the staff is, since there's so many of you now xD.
Just, join in on your RP character and have fun!
I'm sure with talking more with other members, they will get used to your presence and like you!
I'm sure that in some groups there is some talking about the staff and mods, and there sometimes is criticism, which can cause a conflict.
On the other hand, being a part of the Staff team, doesn't mean that you only have to work and sit at the grounds.
You too need to have fun, because if this game starts looking like a job, well..
I'm going off the topic a little bit here, because there is just this thing, which is players not trusting the staff when they're around them, in a way?
You know, trying not to say a bad word and say the wrong thing.
But yes, Staff members SHOULD definitely join RPs. You are a normal member of the community, just like all of us are. You are a player of this game, and what do you do in a game? Play it and have fun! <3