There is no relation between HDR and AA. For example, Risen uses AA and deffered shading technology as well, but there is a way to force AA even if it is not supported officially. nHancer provides some hacks especially for this case, but they don't work for D2 at all. Perhaps the latter copmpletely doesn't support MSAA on floating textures. Well, HDR and MSAA don't mix: its because the resolve is linear. SSAA can do the trick.
