You are restricted by the protocols established by your medical directors.
EMT's and paramedics operate only under the supervision of a physician. These are not "licensed professions". Perhaps they should be, but that is a post for another forum.
Generally, administration of glucose on the inside of the cheek after a needle stick is the only treatment protocol for most EMS systems employing paramedics. Very few permit administration of insulin under any circumstances.
Once again, your heat treatment protocols are constrained, if you are an EMT-1.
Generally, hydration and cooling are your only treatment options. There is no essential difference in treatment of heat exhaustion or heat stroke between a diabetic and non-diabetic.
As far as heat goes, encouraging hydration is the best way to prevent the problem. Salt tablets are issued in the military, but that is a decision for your medical director.
Generally, reassurance, holding their hands or wrists, having them lie down and elevating the feet slightly (eight to ten inches) is all you can do.
Cooling them down and waiting for the arrival of EMS is all you can do.
But more importantly, conveying the extent of the emergency to the EMS dispatcher should be an essential part of your job. If you are an EMT, identify yourself as such. If there is loss of consciousness, tell them that. As for the Glasgow coma scale, it's as useless as a screen door in a submarine.
There is no doctor on this board, John, only other diabetics.
Heat can have very unpredictable effects on blood sugar. Do the diabetics in your company test regularly and have well managed blood sugars? Do they carry glucose tablets with them at all times in case of unexpected lows. Diabetes is very much a condition that needs awareness and self-management. If the diabetics in your company do not know how to properly treat their diabetes with diet, weight control, exercise and regular testing they are putting themselves at risk. Obesity makes diabetes harder to control and a type 2 diabetic who is overweight should be working with their doctor and nutritionist to develop a strategy for healthy weight loss.
Do you know whether your diabetics are all Type 2 or if some of them are Type 1? It makes a difference in treatment. Also all diabetics vary a bit from each other in their control and management regimes. It might help if you could meet with the diabetics and ask them about their own treatment. High blood sugars put a diabetic at risk for complications if they go on for a long time, but are not usually medical emergencies. The exception to this would be if a diabetic is running continually high numbers (300 or over) and begins to exhibit symptoms similar to flu such as vomiting, severe headache, etc. They could be suffering from DKA which is a medical emergency and needs a trip to the ER. DKA is usually suffered by Type 1's only, but occasionally a type 2 can have it.
More dangerous in the short terms are lows. Anything under 60 should be treated. Some people say 70. I would err on the conservative side if the jobs entail anything dangerous like machinery or driving in which case the person should stay over 80. Lows can be easily treated with 2-4 glucose tabs and testing 20 minutes later to make sure it was sufficient. If the person is not able to test and then treat themselves (in addition to always carrying glucose tabs diabetics should have testing supplies at work always) or is not conscious, never try and force anything down their throat even juice as they can aspirate. Call 911. If you have a Type 1 who experiences severe lows regularly (most don't), and this is within your job description, you could ask them to keep a glucogon kit at work. This is an injectible medication that will revive someone who is experiencing severe hypoglycemia and is unconscious.
Oh yes, and diabetics should always stay well hydrated in heat. If they are running high blood sugars this is even more important.