Sure, Tev is a member of the Ebon Blade first, and everything else second. He went to Draenor because of the ebon blade (I like to think of him as the Ebon Blade liaison to the Draenor Expedition.)
Game mechanics aside, Tevruden could have joined the Alliance (he faced the same question Kolitra was angsting over in the Death Kind manga) but he felt that the Horde provided more opportunities to fight.