From the same link above :
(g) Other Requirements— He shall be in possession of a current Flight Radio Telephone
Operator’s Licence for operation of radio telephone apparatus on board an aircraft issued by the
Director-General.
In order to get an FRTOL, one needs an RTR(A)/(P)/(C) from the WPC (Ministry of IT/Telecom).
Is it possible for a non-Indian national to get that certificate ?
(Im not sure, but applying for an RTR does require a Nationality and Character certificate.)
I see this as the only reason why someone who is not an Indian national can not be issued an Indian pilot license.