There are quite a few Eastern Orthodox who believe that no other denomination can lead to salvation. What % of Eastern Orthodox believe this? I don't find it a logical conclusion based on the gospels.
You need to be very careful to understand what people mean. Sometimes it isn't clear, and sometimes catechumens especially get the wrong idea. And sometimes some Orthodox could possibly express different opinions.
What I mean is that you will very frequently hear that we don't limit the grace of God. And that we know where God is, but we don't know where He isn't. Especially according to Romans 2, I believe this is correct. God is going to save whoever He wills, and He wills to save all. So ... I certainly will not dare to speak condemnation of anyone who has any inclination toward Him. (I don't want to speak condemnation of anyone at all, but I'm trying to make my point.)
On the other hand, you might hear that "outside the (Orthodox) Church, there is no salvation."
Some people when they say this, mean that everyone who is saved is added to the Church (whether they were formally within it during their lives or not). So that still is not limiting the salvation and grace of God.
But some people will "hear" this to mean "nobody excepted baptized/chrismated Orthidox will be saved". They could be misunderstanding. Or some might teach/believe this.
I believe when that statement has its roots, it DID mean that nobody outside of those canonically in the Church would be saved, because they were actually talking about those who had the choice to be part of the Church, or had been, but chose to pursue heresies that had been set directly opposed to the Church instead. If for example you have full understanding of the Gospel, but decide instead that Christ Jesus is NOT divine but merely a man whom God sent some special grace to ... well, in that case I believe you DO risk your salvation.
But I don't know any Orthodox in person who actually believe that only Orthodox in this life will be saved. I know of only a few on FB who teach this, and FB in my experience is not a good indication of what Orthodoxy as a whole believes.
