Is their theology as deeply flawed as we see elsewhere? If not, they should probably welcome them, support them and point them in the direction of the muslims.
So, then you must think the Orthodox are not Christians if they need to be evangelized. And just whose theology are you teaching them? Your own? Or is there some "official Protestant truth" that all have to subscribe to? Is it some Protestant "magisterium" that decides who is a Christian and who is not?
For Protestants to call Orthodox un-Christian and in need to be evangelized is like a thief calling cops "bad guys."
Protestants have no business evangelizing Orthodox Russia. There are billions of people who don't know Christ all over the world. But, it 's safer to try to make Russians into "Christians" then to try to evangelize Muslims. You have 1.2 billion of them in this world. But they tend to decapitate Christian ... and that's probably more where their zeal to evangelize stops.