What C6 says is right.
However a lot of unmarried couples do live together and the authorities don't go out of their way to sling you in the nick. In my 12 years in DXB I've only heard of one unmarried couple ending up in the slammer and that was in Sharjah (her husband reported her and boyfriend to the police!). It is still against the law though, so beware.
Re allowances, they are based on cost of eating in the hotel and they have come down as EK negoiates discounts etc, however you virtually never eat in the hotel and I always come back with change. But I wouldn't count on it boosting my salary.
Good luck. I'd recommended it to anyone - but personally have had enough now. I would think LONG AND HARD about leaving your national carrier though.