ACV has definitely been involved in studies (which I can copy and paste links to if anyone is interested?), and the jury is on the side that it does affect post-eating BG levels in a good way, at least for type two. Not just apple cider vinegar, but all vinegars (I believe ACV is the most palatable of them, is all). (Apples - yum! What a shame they are so high in carbs.)
It can be used in particular, is my understanding in the event you do eat a high carb meal - both by having it beforehand, and/or afterwards, in order to help your body deal with the carbs. How you take it also seems to be relevant (ie - pills or the liquid), as in taking the liquid vinegar as a 'wholefood' then, being more effective. (I tried supplements myself, and they had zero affect, so I was not surprised by that information, wherever I read it.)
I have also read that they think the often amazing positive affect of vinegars (all vinegars) on our metabolism is to do with gut biome health, and our general metabolic health (in that we are helped and aided by the biota in our digestive systems to actually deal with the food we eat in a healthy fashion, so for us - it's in insulin and blood glucose regulation in a high carb food environment).
Vinegars, apparently, emulate the affect of eating other animals' stomach and digestive tract contents, which we arguably do not do to the same extent, if at all, anymore, but used to do - well - heaps! This enters the realm of ancestral food and evolutionary biology which I am very interested in, but is not everyone's bag.