I disagree. Just because someone has a low intelligence doesn't mean they are ignorant to the concept of sex and consent to sex.
Have you met or worked with people with really low intelligence. (ie. not the bottom set at your local comp, but someone who is disabled by their lack of cognitive function. Such people cannot live independently or manage their money. They would not be able to organise a prostitute to come on their own. It is not unusual for some people with substantial learning difficulties to really struggle socially with basic friendships. (Ie. lack of theory of mind, the imagination to predict the future, ablity to read facial expressions, to tell when they are being exploited/ bullied, anger management)
For example someone with severe autism may struggle with the idea that the prostitute is providing a service and doesn't actually love them. If the prostitute decides that she no longer wants to service that client then it will cause a complex pychological mess. I am sceptical that the use of prostitutes increases someone's long term happiness.
Rather than organising a prostitute, I feel that care homes need to think what someone's true needs are. Everyone likes a hug, to feel needed, mentally simulated and the warmth of another's human touch. This is very different to having a shag. Rather than employing a prostitute prehaps care home need to employ more carers so that they can chat to clients and meet their social needs.
If someone with major learning difficulties is lucky enough to have a proper sexual relationship then that is very different. In that kind of situation the two people having sex are equal in the relationship and them making love is a beautiful thing. There is no exploitation of anyone.