I understand that you are concerned about overmedicating your pup and causing low blood sugar by giving him Dia-ionX at the same time he is receiving two insulin injections per day.
Dia-ionX is a homeopathic supplement that contains "Aceticum acidum HPUS, Arsenicum album HPUS, Bryonia HPUS, Calcarea carbonica HPUS, Iris versicolor HPUS, Kali phosphoricum HPUS, Lacticum acidum HPUS, Lycopodium clavatum HPUS, Natrum phosphoricum HPUS, Phosphoricum acidum HPUS, Phosphorus HPUS, Plumbum metallicum HPUS, Uranium nitricum HPUS" per their website.
The ingredients in Dia-ioniX purport to help with the symptoms of diabetes (increased thirst, hunger, urination, lethargy, and gastrointestinal upset). They do not promise to lower blood sugar. I do not see anything in those ingredients which would interact negatively with insulin. So I believe that both can be used concurrently.
Please let me know if you have any further questions.