It really depends on the client and their needs and goals. It is not a one size fits all approach. Make sure that you monitor the client for signs of blood sugar dropping, which usually happens during exercise. Weight training is usually more effective for lowering blood sugar levels than cardio, but both are useful. Your client should also check with his or her physician.
from a musculoskeletal perspective, there is no difference to other clients. You do your assessment and make your exercise recommendations based on it.
There are different types of diabetes. People with type 1 diabetes have to monitor their glucose levels very carefully, what I have found, though, is that they are usually very well educated about the diabetes management.
Type 2 diabetes often occurs in people who are overweight, and in that case you may find other complications from a cardiovascular perspective.
In either case, I personally require a physician’s approval. I also make sure that the person understands the degree of diabetes management.
Hope this helps.