Many, many Thai people find it weird that I am a vegetarian with no particular religious underpinnings. Others assume that my not eating meat is based in some bizarre religion...which they conclude is obviously not buddhism. 'If it moves...kill it and eat it and say "aroi maak" - delicious' is the general and quite obvious rule around here. The animals here are either domesticated, or frantically looking for a place to hide.
The majority of Thais are buddhists, but the buddhists here are most definitely not vegetarian (almost nobody here is). In fact, Muslim Thai people are probably less likely to eat meat (since they refrain from eating pork generally).
I have been told that certain buddhist orders here are vegetarian, but the mainstream monks are quite urbane in their day to day lives. They smoke cigarettes, buy pirated computer games at pantip plaza, and on one occasion at least, buy porn from magazine stands. Of course, many young men receive buddhist training here without intentions of becoming career monks.
Conclusion: Vegetarianism is not really a factor in Thai buddhism. I'm currently trying to find out what really is a factor...apart from hanging a little buddha from your rear-view mirror to keep you alive for a couple of extra days in the hell that is Bangkok traffic.