I have no idea what the kosher certifications are or aren't; I'm not speaking to any of that.
According to Wikipedia,
Martini is made from four ingredients: wine, botanicals, sugar and alcohol.
It's a vermouth, i.e. a flavored wine. I see no reason why the bracha would not be the same borei pri hagafen (or hagefen for Sephardim) as other wine or grape juice products.
If I recall correctly, the Kitzur Shulchan Aruch 47:3 says that if vermouth is sufficiently flavored to no longer be called "wine", then the prohibition of stam yeinam no longer applies at that stage and the vermouth can be handled by non-Jews. (The Chochmas Adam quotes this as well, but appears to conclude stringently.) But I don't see that affecting its bracha status.
Of course this discussion refers to Martini vermouth; a martini cocktail is >70% gin by volume (with vermouth, such as Martini brand, as a lesser ingredient) and would be shehakol. Whether the olive (onion if a Gibson) garnish gets its own bracha is a separate question ...