No. I have only seen what I would call violence once in the last 25+ years. Those stories tend to be over-hyped. I've seen countless residents with dementia yell randomly, but not be violent.
My mother has worked in long-term care facilities for around 40 years, and has only seen one violent resident in that time.
Care homes a) have protocols in place and b) can boot violent residents if they are unequipped to care for them.
The people who are really, genuinely dangerous tend to be in very specialized care settings.
Also the nursing home staff in the activities department can tell you which residents to work with, even on the special care units (Alzheimer's and dementia sort of things). They know the residents and know which ones are lonely, what their history is, and which ones will enjoy your company.