This is not the sort of thing that style guides typically address. It is rather a matter of making it as easy as possible for your reader to understand what you are saying, and as hard as possible to misunderstand it.
Your original version is in no way ungrammatical. But it does lead readers, briefly, down a ‘garden path’. As they process the sentence from left to right they are very likely to take the sequence ETG and non-ETG as a conjunct attributive nominal which will be followed by a noun they modify†—perhaps something like:
Decisions made by the CAB apply to all members of ETG and non-ETG organizations ...
The readers are of course quickly disabused of this notion by what actually does follow, and all is well. But this does require them to pause, back up, and re-parse, which is vaguely annoying.
Inserting the to makes your structure unambiguously clear and more easily processed, and it removes a possible source of vexation. It informs readers that you are more concerned with conserving their effort than your own. That's a great gain at the very low cost of typing three more characters.
† If this seems far-fetched to you, it’s because you already know what you mean; it’s exactly what happened to me reading it cold, and I knew exactly what it wanted before I finished the sentence and got to your reviewer’s correction.