I've never lived in Abu Dhabi (only Dubai) so can only provide you with very general information. I will respond though as their aren't many posters in the UAE.
Generally most medical treatments are available in UAE, remicade infusions definitely are. Main issue will be if they are covered by your insurance. Generally in the UAE expats and their families have employer provided medical insurance. You will need to find out what insurance your company provides, what tier of cover, and details of exclusions and caps.
In the UAE you do not need to see a GP and get a referral before seeing a specialist. You can make appointments with specialists directly. Check the Doctor Review section at the bottom of the board, I believe someone has recommended a gastroentrologist in Abu Dhabi who you could try. Finding good doctors here can be a little hit and miss.