No, the past UTI does not make him at greater risk for ketones.
I will try to explain ketones to the best of my understanding, which is very elementary at best..... insulin helps in the proper digestion of food. Glucose is what fuels the body--- but, with insufficient insulin, then the glucose cannot be broken down. We know that with diabetics, this is a problem. When insulin is insufficient, then the body does not digest food properly and the kitty's cannot get proper nutrition, thus the weight loss. To compensate for this, the body starts to break down the muscle and body fat--- ketones are a byproduct of the muscle breakdown. DKA, is a condition that develops when the ketones get at a high level and the body becomes too acidic. With DKA the electrolytes get out of balance. The acidic condition (ph level) is very hard and bad on the organs. DKA can happen very quickly. A BG does not have to be at "High" levels for ketones or DKA to develop-- I have seen cats in PZI go into DKA with BGs in the 200s. It is a good practice, to test all diabetic kitty's for ketones on a regular basis. The keys to warding off ketones are-- fluids, insulin, and food. Anytime a diabetic kitty starts eating less and becoming lethargic, I would immediately check for ketones.
Like anything else, ketones can be treated quickly and successsfully as long as you are testing! So, don't fear this......Just be vigilent, especially when you are lowering the dose. You have a cat that has been getting 8 units of insulin a day and eating lots of food. You are now considering going to 2 units a day and are not certain if he will eat as much. But, to get him regulated, he must get off of the dry food and in doing that he eventually will need less insulin.
You have a tremendous support system here, so just give everyone a heads up when you are going to start your reduction and food switch. AND, get your Ketostix!