Probably not.
The Diamondback is a small-frame revolver, same size as the Detective Special.
The size 10 is for medium-frame revolvers like the Python, King Cobra, and 686, so the holster would be too large and the smaller Diamondback would be too loose a fit.
Looking at the Bianchi chart, I notice some odd information.
As example, the size 10 is also listed as fitting the S&W Model 19 AND the Model 686.
The 686 has a much larger diameter cylinder than the 19, and I don't understand how a smaller cylinder model 19 can be a good fit in a holster that also fits a much larger 686.
Unfortunately, I don't see ANY 5BHL for a 6" barrel that's going to fit your Diamondback, UNLESS they offer a version that's a genuine fit for a "K" frame's cylinder.
The Model 15, 19, and 66 "K" frame has a cylinder almost exactly the same size as the Diamondback, but the frames are slightly larger.
If they actually size a model 10 to really fit a "K" frame cylinder, you MAY be able to get by, but again, the Diamondback really isn't going to fit that well.