Dark chocolate does offer benefits to diabetics, but it's not the same for type one and type two. As a type one diabetic myself, I can confidently say that the two types of diabetes get thrown together quite often, although they are very different.
For type one diabetics, the benefits of dark chocolate include, according to https://pmc.ncbi.nlm.nih.gov/articles/PMC5699188/?utm, things like improved vascular function (blood vessel health), which is crucial since type one diabetics have higher cardiovascular risks. This benefit, while not directly related to diabetes itself, is important because of the increased cardiovascular risk.
For type two diabetes, however, the benefits are much greater. These include improved insulin sensitivity, lower blood pressure, reduced fasting glucose, and possibly a lower risk of developing type two. https://www.endocrine-abstracts.org/ea/0034/ea0034p206?utm