If you don't count background, stunts, or voice work, Vaughn Armstrong is king.
Now part of the reason you see so many actors popping up in different roles is that working under all those heavy prosthetics is very difficult, so finding someone who can handle it is rare (hence why they had to recast Quark's mother).
That's not the whole of it, though, because many of those recycled actors played characters with little or no prosthetics. This was going on since the original series and plenty of other shows before that, as well as shows today. (The various "Law & Order" shows do this a LOT! The "CSI" shows do it too. So did "NYPD Blue".)