Here's something to consider: Did Tolkien himself actually know what Gothmog was?
Think about it. There is one tiny, fleeting reference to him. It's entirely possible that Tolkien simply made up a name for a lieutenant on the spot (choosing Gothmog for fairly obvious reasons) and didn't give him any history or race.
In any case, I resent the lack of a cop-out option,
Fordim. "Tolkien didn't care" would have done nicely.
