It's been a while since I've used it so correct me if Im wrong, but his dps should be the same as a gren sqaud right?
Nah, that was back before the March 2014 infantry combat changes. His squad is now definitely worse than vanilla Grens (not by a ton, but the DPS the officer contributes [which is very little at most ranges] probably also reduces the squad's odds even against Cons at max-range by a fair bit since losing the Gren bodyguards will tank the squad's DPS by an even higher percentage).
Yeah, I used to use ostruppen doctrine quite often and I never had a problem vetting him up. He has slightly less DPS than a gren squad, and he doesn't force retreat when killed, so I find him to be a valuable fighting unit.
Just make sure that he has the ability to shoot enemies from where he is standing and he should vet up at a slightly slower rate than grens.
Yeah, I never really had a problem with vetting him either. Sure, the squad's not amazing in combat, but it's still functionally pretty similar to other basic infantry squads getting vet, and it's not really tough for any of those.