Whatever it is that Chabad does, however they daven, you should know that the place Rav Schneerson ZT”L has amongst them is unprecedented in all of Yiddish history. No one has ever proclaimed that a dead leader is an exclusive emissary from H”KBH, nor has anyone ever made it a minhag to insert said leaders name into teffilos. I don’t care how many Chassidishe seforim talk about “Nasi HaDor” or how many mekoros there are for a meilitz yosher, it’s a new, mudnehdikeh, thing that was invented by Chabad in 1996.
Is it avodah zora? Not for me to decide, others have already weighed in. Is it a new and strange custom with no basis in halacha or minhag that very strongly resembles certain issurim d’orayso? Absolutely.