You can but it will likely limit the number of RPs you can join.  Try asking, you might be pleasantly surprised.  I'm doing or at least trying to do an Arena RP which generally seems to require the use of the RPGO Discord but I'm not going back there.  It hasn't been a problem so far.

I've been in a decent number of RPs here over the years and only a few of them have had dedicated Discords.