I wouldn't be concerned at all about something like this under the older LoME army restrictions. The overall Goblin Town force (whatever the list is actually called) doesn't sound bad considering what I've heard about the basic troop type. So even an OP (but expensive) hero like this in such a list isn't that big of a deal. But with SBG reverting to the old "all Evil" and "all Good" ally format it has a higher chance of getting abused. Nothing to stop the Great Goblin from joining up with Fighting Uruk Hai or Morannon Orcs, for example.

But he would still have to lead a warband of goblin town goblins, wouldn't he? Even if other warbands were allied in? (honest question!)