Not sure there would be much of an edge. By exp and starting skill, a DH IG warrior would roughly the equivalent of a comrade (Though, with HP, and FP). They have not yet achieved the 2000xp that would them to take one of the "Guardsman" roles in OW.
That Is how I would probably handle it: The beginning DH2 Guardsman would draw equipment according to the regiment he was assigned to. Once they have earned 2000xp I would have them "Elite Advance" into an appropriate guardsman class if they were still active in the regiment. (Basically choosing an MOS). Other than that I don't see a Generic IG Warrior having any special disadvantages or advantages against any of the Guardsman roles.