Him being a hobgoblin might be a placeholder for them not having orc or orog models, or just a reasonable use of resources if they're not going to be including orcs in the game.
Being an orog would make much more sense than a hobgoblin being that orogs are of the Underdark, iirc.
The change to hobgoblin works for the story, imo. It acts somewhat as a call back to Dror Ragzlin, giving us a juxtaposed view of hobgoblins. It helps to showcase just how different Blurg is, in other words.
As for changing the name from Grazilaxx to Omeluum, though... I'm at a complete loss. Unless there's a rights issue somewhere at play with the name. I don't know why there would be, but it's all I can think of.
