Can anyone be hired to take care of seniors with Alzheimer's & Dementia?

You'll want to make sure the person is trained for this, but most agencies train their caregivers to work with people with dementia. I'd ask the agency (or caregiver) specifically for references showing that the person has worked sucessfully with someone who has Alzheimer's or other dementia.
You are right to be thoughtful about who you hire.
Take care,
Carol