From what I have heard (boss's daughter is becoming RMT-Registered Massage Therapist), Spa "massages" are very different from therapeutic massages and in my area at least massage therapists in a Spa, while they may have quality training are not required to be "registered". Obviously criteria would vary depending on the area you are in.
Massage "treatment" in a spa would not be anything like massage therapy for disabled. If I were you I would find out from a local care facility or hospital what type of training their massage therapists require and I'm sure they could point you in the right direction. Good luck to you. It sounds like you are looking at a very caring and worthwhile profession.