Marci, what time is your appointment? It would not be the end of the world if Buddy didn't get his shot if he had an early appt.....just feed him as you normally would the night before, and give him his shot and then take up his food after he has eaten so that he has twelve hours before his dental. He is on such a small dose. Then skip the morning shot.
And as you say, his bloodwork is fine! No infections or other health problems. If so, he can afford to skip one shot. I would think your vet would agree that they don't want to deal with him going too low once he is under anesthesia. That is what my vet told me when Tigger had his dental about a year ago. We didn't worry about a shot that morning of the procedure. I am so happy you are getting this done for your Buddy.
Please do check back with your vet's office to confirm though about not giving insulin that morning. I am sure they would agree that he will be fine. Please let us know how it goes with your boy.