The vast majority of the barrels are either made by Shaw or Wilson. Del-ton, Rock River, DPMS, and a few others use Wilson, while others use Shaw. They are both 4140 chrome-moly, same twists, same profile. Both companies offer chrome lined and non-chrome lined barrels. Bushmaster and Olympic are the only complete rifle makers that make their own barrels. Bushmaster and Colt barrels are made of 4150 chrome-moly and a lot of people here seem to have a hard-on for that extra 0.1% carbon content.
As for DPMS, I think the vast majority of their products are great. I have an upper and LPK that are better than the two Bushmaster's I've owned, as in no functional issues and better finished parts. The two things you hear about DPMS fairly regularly are: 1) their bolts have a high failure rate and 2) in the past some of their barrels have very tight chambers. When I bought my DPMS upper, I sold the bolt/carrier on the EE for $100 and then bought a Stag enhanced for $105. Problem solved.
People here get so caught up in the name game, it is ridiculous. If you are buying components from any of the big, reputable names they SHOULD be in spec and compatible with other in spec components. If you happen to get a part that is out of spec, call them and send it back.