This was a concern my wife voiced as well. We had a bad experience medically boarding my last diabetic kitty a couple of years ago. They weren't tracking his numbers well and couldn't get him to eat, so. All a bit dicey, considering how agitated he was at being boarded.
Our neighbor has been pet-sitting for us for about a year now. We trade off keeping an eye on her dogs when she goes. So far, we're working up to teaching her to test and give insulin. Right now it's a bit of a struggle just to get the boys not to freak out and go hide when new people come in the house, but they've seen her enough to be comfortable with her. Now it's going to be working up to getting her to hold Sherlock, then to rub his ears and give treats, then to test. Because she's next door, she can poke her head in periodically to check and test as needed, and to make sure nothing looks hinky.
We'll probably drop the dose while we're gone just to avoid too much risk. It might throw his numbers out of whack, but I'll take that over an emergency.
You might just consider getting your sitter to come over to watch the process, then to help with it, then to take over once or twice with you watching to make sure they're comfortable and you feel good about it. Nothing wrong with being cautious and I'm sure they'd understand.