Can a patient who has Dementia and UTI's exhibit aggressive behavior and hallucinations?

Yup, experienced with my mother.

What helps is curing the UTI. Meanwhile, be gentle and soothing and don't argue about the hallucinations.

Even older people without dementia can experience these symptoms with a UTI. My aunt did, and was totally back to normal after treating the infection.

These behavioral symptoms only occur in the elderly.

I have the same answer as Jeanne. You need to cure the UTI. My FIL gets those, and yes, his personality changes and he has sometimes hallucinated. We've had to take him to the ER a couple times for it, but once the infection is gone, he's back to normal.

Thank you for commenting and giving me a direction to go in..