Their online quote software asks how long you have held a valid licence. I take that to mean a Thai driving licence although I am sure that others on here will disagree. I do not hold an overseas motorcycle licence.
I just did a dummy run through the online quote process and they were willing to quote me around 6,500
for an RE 350 classic.
When I got my insurance a couple of years ago for an RE 650cc they would only give a quote if I'd held a licence for 2 years.
As Bob Dylan said, the times they are a-changing.
The simplest way find out if an overseas licence qualifies would be to ask Roojai themselves, they have an option for English and they will connect you with an operator fairly quickly or give you a call back.