Here is my experience in hua-hin to get both licences:
I went last friday to pranburi to get my car&motorbike licences she asked me to signup in the queue but i told her that i called and was told i not need to signup (i did lie because it was a 60km drive from hua hin) i do NOT recommend to go to cha am.
Anyway i have just 1, 30 days stamp visa and it was no issue at all!
I recommend you to read the questions very carefully as some of them are wrong on the online tests, for example the question about the ambulance, you need to tick (pull over and immediately continue to drive) the online test however say pull to left and stop this is wrong!
Anyway yesterday i did the 2 practice tests i failed on the car because this ****** did NOT told me i can only change the gear 7 times, i needed 8 times, this girl is really evil she said to me you fail in a tone like she is really happy...
But resume of my story you not need a visa in pranburi