Coltrane, bottom line is it is doable, but you have to remember living together when not married is against the law. I am not 100% sure, but I think it is even against the law for men and women to share if you were just friends and no s€x was involved.
You will probably be OK but will likely not get any support from the company if you get locked up over it. I did it when I first moved out here with no trouble, but I also know someone who has been locked up and deported over it. I have never lived in Qatar, but it seems the UAE is more liberal (though I stand to be corrected) - but "caveat emptor".
As far as rosters are concerned, for once I agree with Chandler Bing - no likely help there from Etihad! Also I believe Etihad's accommodation policy is that a couple working for the company share the same accommodation can only claim one allowance. Not sure if it is enforced and maybe if you weren't married you might slide past - but my wife considered a job with EY and was told at interview she would not be entitled to the allowance because I already had it.
Have you considered Al Jaber (Airbus) or Royal Jet (BBJ) in Abu Dhabi? Perhaps possible you might get rostered with your partner at one of those smaller VIP outfits and perhaps their accommodation policies are more flexible.
Good luck.