Should disable people be granted free legal services and representation ?

It depends upon the Constitutional Law and respective Statute of the Respective country.

In India, Article-A of Constitution Law provides free legal aid to protect the rights of certain category of people wherein includes the disabled people as well. Also the the Legal Services Act was enacted for the very same purpose on the basis of Article-A of Indian Constitution to meet and serve its objective that no on should suffer and deprive his/her legal right because of incapacity or disability.

Further, I am sure there are so many Advocates willing to extend their help for the real needy people as a duty towards Society as an Advocate. Thanks.