Flash photography controls dynamic range by reducing it before the image is committed to a file or negative. I made some HDRs out of bracket sets shot in a sandwich shop and a small museum that simply look like flash was used followed by some curve control and maybe a plugin. There is a video on Youtube that points out they results are not exactly the same. Flash is directional and controlled by a whole set of techniques. Indoor HDR lets you show both the inside and the outside, into shadows, eliminates hot spots etc.