I've added to this collection since this picture below was taken, and, drawing from personal experience, I'd maintain that some leakage is normal. Not leaking is much farther from the norm.
The only one I've ever seen not show signs of gas leakage in this area is .835" JP gas block I had to hone to fit to a 24" Kreiger barrel, and that one leaked back around the gas tube entry bore. Production FSBs are not hand fitted or honed for a flawless fit.
Every one of these rifles, Armalites, Bushys, Colts and a few I put together myself, as well as several spare uppers I have, show some sign of gas leakage around the FSB. The SS barrel makes this example look more severe than it ordinarily would with a Parked finish.
Further, this example also looks more like a small amount of gas blew a large amount of (stained) oil out from under the FSB. Looking closely at the photo, it is very obviously a liquid stain, not just dry gas. The bore/gas port either contained an excess amount of oil or solvent, or the assembly/shipping oil was still present on and around the FSB in excess amounts. Just like a very small amount of blood can go a long way, I'd suggest that this oil makes it look much worse than it really is.
By all means, call DPMS, but don't think they're just blowing you off if they act like it's a non-problem, since I'd expect you to hear them tell you the same thing.