He's probably a top 5 Russian NHLer, but definitely not if you include guys who played for the old Soviet Union.
This is how I would rank them:
1. Slava Fetisov
2. Valery Vasiliev
3. Alexei Kasatonov
4. Alexander Ragulin
5. Sergei Zubov
6. Vladimir Konstantinov
7. Vladimir Lutchenko
8. Sergei Gonchar
Nikolai Sologubov could also have been better than Gonchar, we just don't know because his played against questionable competition.
Gonchar is almost certainly one of the top 5 NHL Russian defensemen. Who would round out the top 5? Andrei Markov? I can't even think of a 5th (Kaspiritus isn't technically Russian). Edit: Er, I mean Fetisov and Kasatonov did play in the NHL, but I still don't really consider them "NHL defensemen."