Considering the number of gay travelers in Thailand and the high volume of action they have with locals, it's inevitable that monkeypox will soon spread to Thailand.
I think it's impact though will be limited. As scary as the symptoms of that disease are, it's rarely life-threatening.
I think in a first moment, when it starts getting media attention, there might be some hesitation from local guys to hookup with foreigners on apps. The sauna scene might also be curtailed. I don't think it will really affect the paid-sex market.
With time though, as more foreigners get vaccinated and the vaccine will eventually be available in Thailand, it will just end up being accepted as another STD.