Hi Corinne,
It may be a matter of trying formulas and seeing which one finally kicks in. SMS may help, although the progressive weight loss suggests maybe Zhi Bai Di Huang Wan might be a good place to start.
Any chance of pancreatitis here? It's odd that a raw diet hasn't dramatically helped his blood glucose, which makes me wonder if there is something damaging his islet cells on an ongoing basis. Yi Guan Jian may help with that if the pulse is more fine and weak; or SMS if the pulse is more robust. ZBDHW goes with a robust pulse, too
If additional testing does show ongoing pancreatitis and islet cell damage, then Gymnema and Cornsilk (from Natural Path) may promote their partial regeneration
Hope that helps!
Steve