Snowball isn't Lenin!!!
The review there says that Snowball is Lenin and Napoleon is Stalin. First, I hope that it's the review that's wrong, and that it's not how the movie depicts them, because that would mean the movie is wrong. In the novel, it is quite clear that Snowball is Trotzky. Old Major is a cross between Lenin and Marx, I'd presume.
While I'm against a review spelling out who which character is, I believe that in the novel Orwell spells it out quite clearly, as he talks about the speech style of each of the two pigs, and their public rivalry.
Btw, I find it awesome that their voices are those of Kelsey Grammer and Patrick Stewart. Each of them is unique, yet they were always somewhat interchangable in my own mind. I know they worked together at least once in the past, when Grammer appeared at the end of a Star Trek episode, as a captain whose ship had just got out of a time loop. Though, who knows, maybe they never even met.