I asked this question when I went to see Dr Hakim in London a few months ago. He said that he considers them to be the same, but that it doesn't really matter if they are the same or not, as they are close enough. He went on to say that they need the same treatments and therapies, and that everyone ewith HMS/HEDS is affected in different ways, and to different degrees.
I liked this answer as he gave me his personal opinion (yes, they are the same) while at the same time saying that if someone else says they are not the same, that can be true as well.
I hope this helps
Diagnosed HEDS December 1st 2005. DD1 (20) HEDS and scoliosis (now corrected by surgery), diagnosed June 2006. DD2 (18) mild HMS. Son (11) some hypermobile joints, poor muscle strength and seems to be developing scoliosis as well, woopee!