I have been down through southern thailand all the way to the tip then to penang, malaysia to kuala lumpur, malaysia a couple of times.
There is tension down in the south so I believe one should take caution especially if they are not familiar with thailand and traveling. But that aside I found everyone really cordial and very helpful. The south of course is mostly muslim as opposed to rest of thailand and even if its not since someone reported the numbers dispute that, the feeling is of a Muslim community especially the further down you go.
I think the best bet as you mentioned is to get a lead or a name of someone to see or train with and begin there. So you have a set agenda then you can fan out from there.
There is alot of sila/silat masters and some are open to teaching and some are not to outsiders.
I am finishing a DVD called the village of the keris; the art of bun dai sara on a southern thai master who teaches how to make the keris as well as the art of training and learning to use the keris. He was very open and nice and introduced me to two sila masters.
If you watch the dvd you can get a glimpse at sila and keris training as well as look at footage of malay systems since malaysia has a huge influence over southern thailand because of its close proximity.
of course as you know Chaiya as in chaiya boxing is called southern boxing because Chiaya is in the south of thailand. But its own thai system and to doesnt resemble or train like silat though others see it differently. The systems that look most like silat are the northern systems and those resemble and have a flavor all their own as well as some closeness to burmese systems.
I found many interesting masters in the south so its well worth a trip. Just plan it out ahead of time the first trip so you make friends and they will give you info and steer you clear of any problems from there you can venture out and know the terrain better without any further problems.
If your friend personally contacts me I can possibly help with some leads depending on what he is looking for. But i suggest taking a look at the dvd before he goes if he can, so he gets an idea of the area and teaching, it will be very helpful to him. you guys can also email about the dvd if you are interested, the site
www.thaikeris.com should be up in the next week or two I hope.
Very interesting and worthy topic by the way.