I can see how a learned farang teaching another farang may be useful - but only in a supplementary way. I've done it myself, at times...
I have managed to teach my lazy friend some things that he couldn't or wouldn't understand otherwise, by explaining in a way that is clear to both of us, and only because I had already sussed out the same questions that he has for myself, or with the help of a Thai teacher or friend. When there is a question of "how do I express this thought?" - a farang who is quite knowledgeable about Thai language can be a good shortcut, sometimes. But I would stress that can work only for very specific questions (such as how we do it on this forum, and even then, we usually require Khun Nan's very generous assistance).

I wouldn't consider that a recommendable path for school study, if for no other reason than that a farang student should hear the "music" of Thai language from native Thais. Do you really want to replicate the sound of a farang pronouncing Thai? Only if that farang actually sounds like a Thai, of which there are scant few. How could a novice even know whether this teacher possessed proper diction, or not?
Also, the following phrase casts some serious doubt in my mind about this premise: "...such as why the word Hmak (
หมาก) has a low sound when the first consonant is a rising tone consonant..."
Well, there is no such thing as a rising-tone consonant in Thai language. The proper definition is "high-class consonant," which by itself does not determine the tone; the class is just one of a couple elements that determine the tone of a syllable. Perhaps that was just a typographical error - or, is it a fundamental flaw in the pedagogy?
If I were a novice being taught about "rising-tone consonants," I think that I would be very confused, perhaps irreparably so.
And, let's face it: farang students (especially those who would study with a farang teacher, instead of a native Thai teacher) do consult romanized transcription, whether anyone wants to admit it, or not. So, what is the point of writing that word as "Hmak," when the Thai
ห is merely a silent tone-determiner, as Markin notes? Seems to me that can only lead to mispronunciation, and casts more doubt on the proposed method, making one wonder about the comprehension of the person doing the teaching.