Conquest of the Horde

So, there's a tribe of Tauren named the Highmountain tribe. Apparently, they're on the Eastern Kingdom continent. Is it possible to play them?

http://www.wowpedia.org/Highmountain_tribe

*shrug* I play made-up tribe that lives in Silithus, but its yet unapproved so I won't give too much on that.

I'd say yes;

1. Is it a race/faction that can feasibly blend-in with one of the player factions?
   -Check.
   
2. Is it a race/faction that is currently in one of the over-arching "main villain" group?
   -Nope!
   
3. Can your character cope with the fact they came from another faction?
   -Seeing as it's not another faction, I think you're set as far as this is concerned!

Source

Read about Trag. They didn't originate in the Eastern Kingdoms, but migrated and explored it. Though, I do see you never mentioned it that way. Just to inform people, so as there's no confusion.