IIRC, wasn't even "Tiberius" originally just a joke of Gerrold's, based on the miniseries I, Claudius airing around that time?
If so, it's quite a coincidence, considering that the main character of Roddenberry's first series, The Lieutenant, was US Marine Corps Lieutenant William Tiberius Rice. Roddenberry reused character names a lot (cf. William T. Riker), so I always figured "Tiberius" came from him.
Well, I'm friends with Gerrold on Facebook. I suppose I could just ask him there.