This doesn't sound that useful to me. It doesn't indicate something well-defined about the question, which is pretty much the point of tags.
As rumtscho points out in Can we handle questions about diabetic-friendly food?, questions about cooking for diabetics need to clearly specify goals (e.g. "low-carb"). If we want to tag those questions, we should probably do it based on those specific goals, not the vague "diabetic-friendly" notion.
That would put answerers in the awkward position where their answers would be assumed qualified answers concerning suitability for diabetics - and unless I am mistaken, unlike a clear allergy where its is black-and-white about avoiding a contaminant or else, judging that really sounds like a health topic and/or like something that takes a health professional, trained diet cook, or otherwise specially knowledgeable and/or trained person to do.