pukunui
Legend
They do have difficulty cloning Force users. That’s a big plot point from Ep 9 that they’ve been building up through the various shows now.Any reason to think that he did actually survive? After all, we know the Star Wars universe has cloning technology this version of it doesn't have any difficulties with cloning force users...
Palps has spent years trying. Snoke was his best attempt. But he’s still had to settle for what seems to be an undead body (but is probably just a badly decaying clone body because his original body would have been vaporized).
So no, I don’t think the Grand Inquisitor in Rebels is a clone. He’s either still alive, or someone at LucasFilm has messed up badly.