Does anyone know if a Thai citizen is eligible for a visa on arrival for St. Lucia? Thanks.

Yes they are eligible to apply on arrival, but they could be refused

http://www.govt.lc/services/apply-for-saint-lucia-non-immigrant-visa

I suspect that carriers may have an issue and don't forget to research the transit visa requirements enroute.

Thanks! That's very helpful. My wife is a US green card holder and it's just a 5 day trip with me to Sandals with return tickets, a job to return to and plenty of cash so she shouldn't be refused.