I don't know about that exact route (or air travel), but my current guy is from Laos, and has been basically living here for the past 7 months. Only thing I can say is ensure your guy has an address and phone# of where he'll be staying in Thailand, otherwise they will refuse him entry. Happened to Leo first time he tried coming here at least.

Aside from that first time, he's never had an issue crossing the border. They've never once asked for proof of finances, or anything. One time he got a VISA from the Thai embassy, but aside from that has always just came in under 30 day exempt stamps, as he never stays more than 30 days anyway.

still waiting for him to get denied entry for staying more than 6 months in one year, but hasn't happened yet. Maybe things are more lax for Asean citizens. So far though, he just says he'l coming to visit his "faen" (boyfriend / girlfriend), and no issues thus far.
n