There's no scientific evidence as of now that says Russian Blue Cats are hypoallergenic.
However if a person is Allergic to most cats then the Russian Blue Cat seems to affect those people less so in my opinion Russian Blue Cats are Hypoallergenic.
Russian Blue cats produce less glycoprotein Fel d 1, which is one source of cat allergies.
The thicker coat of a Russian Blue Cat also traps more of the allergens closer to the cat's skin.