Oh absolutely. There are a TON of cats that start out bouncy (probably most of them) and then get well regulated.
Just off the top of my head . . . Gabby, Max, Eddie, Gracie, shoot, I need to be looking at the current posters and don't have another window open. But the answer is definitely yes. The bounciness comes about if a cat has been in high numbers long enough for their body to get used to that as a normal. Many cats have been diabetic for a while before they got diagnosed. Then when you finally get them into normal numbers, they react to it. But the more time they spend in normal numbers, the more the bouncing will lessen - both in intensity (not into the 500's, anymore, for example) and in duration (maybe just a mini-bounce of 3 hours and a high of 130).
Being bouncy doesn't mean that you won't get him regulated, Stacy, so don't worry about that one bit. It's a process.
One thing that some people do is to learn to "feed the curve." It's a method of feeding that does a couple of things: you feed the cat to prevent fast and dramatic drops - those alone can trigger another bounce, and you also feed to be able to get enough insulin in the cat to bring down the higher numbers. A good post discussing this is on the
"Where Can I Find?" post, look to the bottom for "feeding the curve."