From personal experience, a family drove a car, no licence, got invoved in a minor incident.
The car was insured for anyone, the insurance guy came out, the car was later fixed.The Police arrived and took details. At no time was a licence mentioned by anyone. The drivers of both the vehicles had NO LICENCE.
Now, lets be clear, I am not advocating this nor am I saying this is standard practice, everything in Thailand is inconsistent. This is my experience only.A licence is a legal requirement to operate a vehicle in Thailand.
The licence system and enforcement is a joke.Its cheaper and more convenient to pay a 400bt fine for no licence (example) than take the nonsense test.