Any that has an ability to be made useful to the Sabers can enlist and train under the most elite of the Voma - however only Voma can enlist.
They are the Sovereign's right and left hand, they do as he desires, when he desires it - mostly for reconancence on the Rawkken’s borders, scouting for information and slaying any and all that stand in their way.
Whilst the Voma have the assistance of the Kamina’s Iron Maidens due to their treaty, they can’t be used to a great deal of their war efforts and require agents of Saber to help aid in the war for their homeland.