DHSS = Dept Health & Social Security part of IoM Gov(see www.gov.im)
The burial register was transcribed by IoM Fam Hist Soc and you can buy a copy - I think also microfilmed by Mormons (as is the sep book with Memorial Inscriptions)
What year are you concerned with - there was no poor law on the Island and paupers would be buried in their own parish (probably with pauper noted in parish reg) until Douglas and then Braddan House for Poor (see www.manxnotebook/history/poor/history.htm) which as Nigel said from mid 19th C buried its dead in Braddan New