not to detract in any way, but Germany was operating Soviet Mig-29s alongside NATO kit for years (maybe still?) after reunification. So if anyone could do it...
For example, Turkey recently declared that they will buy some kind of Russian advanced anti-aircraft system so they probably think that it will be cheaper in long term than buying it from a NATO member. Yet, even in this case they had quite strong tensions with NATO and it is not clear if Germany wants to have (and can afford) similar tensions with NATO, even if these Russian helicopters are technically better.
Introducing Russian (or other non-NATO stuff) would require extensive trainings, quite possible new sets of tools, and who knows if any Russian stuff could be made to interoperate with NATO technology.