It's important to note that this only applies to the social services aspect, not to the medical aspect. If a person is found inadmissible because they're going to cost a lot of money to social services, special education, or respite care, those types of services, then they can produce a letter explaining how their family is going to help, or that they're going to hire private individuals.
My experience is that, in most cases, they are not successful because the health authorities are very reluctant to accept this type of undertaking. Having said that, I have been successful in a few cases, but the vast majority of the cases where the fairness letters are provided, they're not accepted.