I should note that under the terms of the compact, all Biotic Drell (and there aren't all that many) that are born on Hanar worlds are required to serve the Hanar, and are not given nearly as much freedom as their non-biotic families. They serve generally either as Assassins or Bodyguards, but they [i]do[/i] serve. Thane is only capable of following Shepard because he is old and has retired from the assassin business. Kosso went to great lengths to get out from under the thumb of the Hanar and Daryna was spared from the Compact by being born on Omega. Kolyat was not Biotic and so free to do largely as he pleased.

Thats not to say you [i]cant[/i] make a Drell vanguard, but if you do a good reason for why he is not serving the Hanar should be prominent in your bio.