I do not think your dad has become susceptive to have UTI because of bladder cancer. I think cystoscopy itself is invasive enough to cause UTI for some patients. A case in point, the web site of Mayo clinic says some urologists prescribe antibiotics before or after cystoscopy. My urologist is so busy and I see every patient who has had cystoscopy comes back with a small towel sometimes with blood. But, he has not given me anti-biotics.
Having said that I have heard a well-known urologist was saying about the field-effect as a cause of high recurrence rate for non-muscle-invasive bladder cancer. It is considered that most bladder cancer is caused by long term exposure to some toxin in urine for many years. So by the time a cancer develops at some part of the bladder, the other part of the bladder, ureter, and urethra have been exposed to the same toxin for many years. So, those surfaces have become susceptive to have bladder cancer. This is called field-effect.
Best wishes