It appears to be. I didn't ask Jack specifically about this, but he assured me that the Russian 6N2P was a drop in replacement, and from what I've read, I think the Russian tube is considerably more problematic.
As I understand it, the only difference between the 6DJ8 and the 7DJ8 is that the heater on the latter tube is supposed to run at 7.3 V instead of 6.3 V. According to a discussion on Tube Asylum, this is within the allowable variance for the tube. He says he has Amperex 6DJ8s that are actually 7DJ8s.
Tubes Asylum: RE: The Flying Saucer by TimB5881
I've read two "explanations": one is that the heater runs at a lower voltage and therefore the tube should last longer; the other is that the heater draw is within tolerances and is no issue. In the short time I've been trying them, I haven't seen any evidence of a problem, and the discussions seem to indicate that this is a safe substitution.
Then again, I'm a musicologist and know nothing about electric circuits; my best guess is that they're some form of magic. You might want to check with Jack. Or Jamato8.