I am a senior manager for a company which has six medium sized homes for older people. I asked -through our company Facebook page - for comments on this subject, attaching an online article from The Guardian. Of the responses I got, staff working in the homes were without fail in favour of this! It was noticeable that the staff responding were those whom I know to be responsible, kind and caring people. Other respondents who do not work in the care sector felt that the camera route may be too intrusive, asking us to be more thorough in our recruitment. As already noted in this thread, this is nigh on impossible as people attending interview are very clever in presenting the persona we want to see - as if by magic, as soon as their six month probationary period is over they become very different people.
My personal feeling is that yes, cameras should be used in certain circumstances - we have in the past caught a thief thanks to a covert camera placed in the room by the Resident's family (without our knowledge) - by the way this turned out to be the person we least expected!