No, they are not here.
All the monkeys on Samui were exterminated. They only left some to work on the plantations. Then it became illegal and became a rarity.
Now there are a small group or two, but they have only been seen a couple of times. These are either escaped or released ones. There is, of course, no talk of population recovery.
Seeing monkeys on Samui is harder than encountering the same python.