KC's got a point actually. Gayle's yet to score a hundred when facing a truely world class Test spinner. Vettori certainly isn't a class Test spinner, and the only other spinners of note he's scored hundreds against are Boje (made 302), Panesar (made 109) and Swann (made 102), none of which are top class spinners. The best is Swann, and he's nothing more than decent. He did make an 88 in India against Kumble and Harbhajan, but that was on a very flat pitch, and he made another 83 against them, but that was on another flat track in the 1st innings.
In ODi's he made a hundred in India on a pitch where India chased 325, and the figures indicate he didn't play Harbhajan too well, as he only went for 30 from his 10 overs, with Kartik also going at only 4.6 an over. He eventually got out to Sehwag as well. Also made a hundred at Napier against Vettori, who is a very good ODi spinner. He's also made a few hundreds in India, but batting first up against the new ball in India is always the best time to bat, and all but 1 of his hundreds have come on 300 pitches.
He's yet to make a hundred against Murali in either form, never made a hundred against Warne, didn't make a hundred against Kumble in Test cricket. The only genuinely good spinner he's made runs against is 1 hundred against Vettori in New Zealand in an ODi. There's certainly no statistical evidence to prove that Gayle's good against spin.