<i>Is anyone referred to as the The Rebbe by anyone other than his Chasidim?</i>
Highly unlikely for a technical reason. The way Rav Ahron Kotler and Rav Moshe got that title was because at public events where many Roshei Yeshiva were present the other Roshei Yeshiva would refer to them as “The Rosh Yeshiva” By Chasidim they don’t have Agudah convention type events. Nor do they make hespedim with many Rebbes from different groups present. Therefore they don’t really have the opportunity to informally crown anyone with that title. (perhaps because the litvish crowd doesn’t really have neutral gatherings with many different Roshei Yeshiva present anymore either that is why the title is no longer used) But what Rav Ahron Kotler was to the other Roshey Yeshiva the Satmar Rebbe was to the other Rebbes