Essentially what it comes down to here is how much a player helps the overall team defense. It doesn't particularly matter how you keep the other team from scoring as long as you keep the other team from scoring. Man-to-man stops do count on the scoreboard, nor do blocks, nor does help defense, nor does number of times you intimidated somebody coming into the lane. That's all irrelevant, and points are all that matters.
Well, the best way to look at a player's impact on a team that takes into account everything they do, whether it's in the box score or not, is an on-court/off-court +/- measure. I do dislike +/- for a single game, but over the course of a season or two there's enough data to start to wash the randomness out and get a true picture of what's going on.
Chuck Hayes, over the past two years, has been worth 4.0 and 3.5 defensive points per 100 possessions. Samuel Dalembert, over the last two years, has been worth 3.4 and 1.6 defensive points per 100 possessions. There may be some noise here, but this suggests that the totality of what Hayes does saves about 3.75 points per 100 possessions, while the totality of what Dalembert does saves about 2.5 points per 100 possessions. And we don't have to argue about the relative merits of totally subjective things like intimidation in the paint and anchoring a team defense when we look at these numbers, because the numbers take that all into account when they look at the whole big-picture result.
A lot of people around here seem to be fixated on the fact that Hayes isn't tall and doesn't block a lot of shots and extrapolate that into the idea that he can't be a good defender. But the numbers show that he is actually quite a very good defender and that this value as a defender shows up as an overall team improvement. This is not a dismissal of Dalembert, because he is a good defender as well, but available evidence suggests that over the past two years, Hayes has been a bit better.
As an aside, when looking at the overall on-court/off-court +/- numbers (offense and defense, arguably the most important number), Hayes has been a net +5.35 points over the last two years. Dalembert has been -1.45.