It's assumed that any of these Brands actually make the barrels? I got the impression most purchased parts out and simply assembled.
Very likely the guys who ship RRA barrels also make DPMS. It could be deliberate, or maybe they shipped one by mistake, but overall, saying Rock River > DPMS without knowing where barrels are really coming from is somewhat, umm
naive.
If it's a milspec barrel, gotta ask what the odds are of it being much different even if it was from somebody else. Chromed button rifled and 2MOA is a commodity item, not something special.
And, we're taking the dealer at his word.