Could diabetes cause black spots on the feet?

Yes. These are eschars (from dead tissue). They are most often due to diabetic neuropathy, in which there is loss of sensation - particularly in the lower extremities. This loss of sensation leads to lack of recognition of injury, by the patient, along with poor blood flow to the site in order for adequate tissue repair to occur. Untreated, gangrene may set in and, in extreme cases, amputation of a foot or even lower limb might be needed.