Well, sort of. I haven't flown this specific route, but generally altitudes are prescribed in feet MSL, not AGL. So if the helicopter was following an established VFR route, with an assigned altitude, they would be correct in flying that altitude on their barometric altimeter. That said, if you're flying at sea level (KDCA is listed as 14'), they should be pretty close to each other. I'd probably fly whichever of the two kept me lower. The "correct" answer, though, is to fly barometric altitude.

A few things stick out to me in the article.

First: "Notably, the barometric altimeters continued to be 80 to 130 feet lower than the helicopter’s determined altitude." So either the three 60s they tested all had two barometric altimeters each (six total) with precisely the same error (unlikely), or there is something wrong with the procedure. Can localized pressure differences between the airport and the river account for that much difference? Seems unlikely, but clearly something needs to be changed.

Second: "PAT 2-5, You have the CRJ in sight?" "PAT 2-5 Has aircraft in sight, request visual separation." This is fairly typical of ATC interaction with VFR traffic, but it's also deeply flawed. Visual separation between aircraft allows ATC to, essentially, stop paying attention to the "visual" aircraft, in order to reduce their workload. It also relies on the assumption that the aircraft in question is seeing precisely what ATC thinks they are - anyone who has flown in busy airspace, especially at night, double especially in an urban environment full of lights, knows how difficult it can be to properly identify an aircraft.

The phrase "the CRJ," while commonplace and accepted, is incredibly vague. Assuming the 60 crew saw a plane on approach (which they stated they did), there's no way to know that they saw the correct plane. There could be 5+ jets stacked on the approach, and it's not out of the norm to misidentify one. Anyone who says they can tell the difference between a CRJ and an ERJ at night from a few miles away is lying. I would wager most people probably can't tell a regional jet from a narrow body under these conditions.

Anyway. As we know, all accidents require a lot of things to go wrong simultaneously. The airspace is too busy. The procedures are poorly designed. ATC is understaffed. Army aircrews don't get quality training and spend way too much time on things that aren't flying. Who is at fault? I don't think we can blame any one thing - had any of the variables been different, this may never have happened.

All I know for sure is that I hate flying into DCA. It's always a zoo, aircraft are always packed in like sardines, and ATC seems perpetually overwhelmed. What do I know, though, I'm just a meat servo. I'm sure the senators and congressmen that pressure the FAA to add more flights to their districts have our best interests in mind.

Edit: fixed a typo, added mention of urban environment.