The fact is, there is no law against discrimination on the basis of nationality in the UAE. Quite the contrary in fact! The UAE government has a program of "Emiritisation" to encourage more of their own citizens into the workplace.
It may well be that Indian ATCOs could do the job sufficiently well at Dubai or Abu Dhabi, but if the GCAA wishes to grant licences to western ex-pats and locals only, so be it. It's their country and they make the rules, just as India makes rules which, so it seems, will soon see the end of ex-pat flying jobs in India, and which already make it all but impossible for non-Indians to invest in Indian businesses.
Railing on Pprune at the injustice of "western only" hiring practices will do nothing to change the situation.