ok, well if it's included in the contact it would normally be to your benefit.
i would suggest getting them to add it to your basic salary, instead of it being a "perk" - as a perk it would not form part of or be calculated in your final gratuity payment (gratuity = a bonus that you are entitled to at the completion of the full term of the contract).
for example if they offer you 1,000 AED basic and 2,000 AED "station allowance", your gratuity payment on conclusion of the full contract would only be based on the 1,000AED (not 3,000AED).