In reply to Niranjan.

A drone can indeed be both. Either a part of the IoE infrastructure, for aggregations and transmission of data or as an IoE node itself. It can act as a router of information aggregated from nearby drones (think clusters).
Lastly, if once again you envision a cluster of drones, one could indeed act as a gateway for the others or depending on the data/processing load, each could also have it's own gateway. All of this is predicated on the use case.