Groovrider is correct. Uldren is a Risen, and will not be a Guardian unless he joins the City and falls under their compartmentalized system of Classes. You are correct that the Uldren we know would most likely be a Hunter. However, lore shows us that a Guardian’s personality can be extremely different from that of their previous life. As an example: when the Awoken discovered the existence of Guardians, it was because they caught an Awoken Guardian that was a man they knew in his previous life. They tested him and discovered he was nothing like the man he was before being revived. This means the new Risen Uldren could have a very different personality and could become a Warlock or Titan. Also, Uldren killed Cayde. As a Risen, he is an entirely different person. He is no longer Uldren. Should he appear before the City, the Guardians will have to figure out what to do with him, and they could decide to count him for Vanguard if he becomes a Hunter.

Uldren is a lightbearer, like the Drifter. He is no guardian.