I'm not sure that I think there's a direct comparison to hardness and dent resistance, but the crush test is spot on. I'll admit that my material knowledge isn't significant, even though I hold an engineering degree, but I think that there are far more significant factors.
I'd like to see the crush test examined to include a long section of tube. If you used a piece long enough to eliminate any end constraints and loaded it at the center it would be the closest approximation of a dent.
Also, some impact testing vs. controlled applied loads might be in order. I realize that it's difficult to calibrate a hammer, but you could simply drop a specified weight from a specified distance.
Also, does bending have any effect on the dent resistance. How about the same tests on a bend?
I think your on the right track and am only offering a few other ways to get additional results.
