Laminitis, early or late, usually presents in BOTH front feet and as reluctance to move, tenderness, "ouchiness" or short stridedness. It does not usually present with unilateral heat or lameness. A finding of heat in ONE foot, if the finding is consistent, simply means something is causing inflammatioin. An abcess is a much better fit with the symptoms given.
I am not quoting a website, the above is based on my experience with horses with laminitis.
All overweight horses are not laminitic, and there is a wide variance in the amount of over weight individual horses can tolerate before becoming laminitic.
There's the added detail that the horse has a history of hind end lameness, and an experienced observer thinks the lameness may originate in the hind.
So I would caution posters against attempting to diagnose this horse over the internet by the owner's description..
However, I will say the symptoms do require immediate attention. If you can get the farrier out quickly, do so. See if he also finds heat in the one hoof. Have the shoe pulled and have him look for an abscess. Farriers are often very good at spotting lamenesses, so I would also job the horse for the farrier and get his opinion. Based on the farrier's assessment, decide whether to involve the vet.
Good luck, and do post back and let us know the outcome.