YES! It absolutely does sound like DH.
I had DH for 3 years and no Dr. dx it! I researched myself and went gluten-free and low and behold my rash disappeared and never came back (unless I get inadvertently Glutened!).
The Prednisone (if by pill) will definitely slowly help but will mask whatever help the gluten-free diet is giving you. If after finishing with the Prednisone you don't get DH back, then the gluten-free is helping. The DH is a delayed reaction usually and doesn't show up immediately after eating Gluten - it can be 3 days to 3 weeks later! As you become increasingly "healed" and gluten-free it will be less (I'm at 3 days).
Some noteworthy things about DH: It is "bilateral" - ocurring on the same place on both sides of your body at same time (both elbows, both shins, etc). It is the ITCHIEST rash you've ever had. It is like little pimples or blisters with clear fluid inside that still itches even after they've been broken open by scratching. They are very "shallow" and break open with the least little bit of scrathing or rubbing. They scab easily and still itch. It can occur ANYWHERE on your body, contrary to what some articles/researchers/Dr's say. I had it EVERYWHERE on my body EXCEPT my scalp and neck/face: I had it on my palms, crotch, stomach, chest, back, thighs (outside only), shins, ankles, feet, back of hands, armpits, arms (all over), buttocks.
I know when I've been Glutened, but usually can't identify what exactly it was, although usually I can associate it with eating at restaurants.
When I get really bad (from inadvertent glutening) I take Prednisone for a couple of days to take the edge off and keep it from spreading - it will spread from scratching too much. Then I use prednisone cream for a couple days and eventually it all scabs. I have scars everywhere though that will probably never go away - little white circular scars that most people think came from chicken pox (hence the name H= Herpetiformis which comes from herpes - one of which is chicken pox - "zoster".)
Good luck. The only way I found out that it really was DH was going gluten-free (not just Gluten-light) for several months and realizing that the rash did not return.
GOOD LUCK and TRY to not scratch. Eventually my Allergist did some research and agrees with my own diagnosis!