Does it matter to be certified? Is it necessary?
No, you didn't need to be certified in anything, you only need to follow your state's licensure laws.
Is it ethically responsible? Yes, certification from a knowledgeable, reputable therapist who practices that specialty themselves is very necessary.

I am a researcher. I had done a lot of research on different training options - some long, some short. And knowing that this was what I wanted to practice, I decided on a robust program that would really teach me enough to practice Thai massage.