He was a not-terribly-good spinner, from all I've heard; only started to become a bowler who was taken seriously when he started bowling seam-up.
Either way, the question of "have there ever been any great left-arm spinners apart from Vettori?" is one of the more odd ones I've heard posed recently. There have been many left-arm fingerspinners who've enjoyed miles more success than Vettori has. The days of fingerspinners, left- or right-arm, being able to dominate all over the globe are gone, however, and went a long time ago. It is no longer possible for a fingerspinner to have sustained success in England or New Zealand, it hasn't been in Australia or South Africa for a very long time indeed, it virtually never was in Pakistan (except briefly in the days of Iqbal Qasim and Tauseef Ahmed then later Saqlain Mushtaq), and at the present time even the original spin-haven of India produces less spin-friendly Test tracks than used to be the case. Only Sri Lanka really remains the proper spin-haven it should be.
All of the great English fingerspinners - most of whom were left-armers (Peate, Peel, Rhodes, White, Verity, Wardle, Lock, Underwood) - date from the days when wickets in this country were uncovered. In the days since wickets in England have been covered, only subcontinental fingerspinners (Bedi, Prasanna, Kumble, Harbhajan Singh, the aforementioned Iqbal and Saqlain) have ever enjoyed much sustained succes. There hasn't been a genuinely successful Australian fingerspinner for many decades, and there's only ever been one from South Africa (Tayfield) and one from West Indies (Gibbs), both of whom are also a long time ago now.
In modern times the only bowlers who've enjoyed widespread success Worldwide have been wristspinners - Muttiah Muralitharan and Shane Warne. And if anyone thinks there's likely to be another one of those two any time soon they're asking rather a lot.
