I skimmed this PDF and I was impressed with some of the things it covers, that you don't typically see in print. A lot of it had to do with personal care attendants and whether or not they were comfortable with helping with sexuality, ranging from masturbation to positioning the person for sex, clean-up before and after, etc. Very intriguing. This PDF isn't specifically meant for OTs, but I think has a lot of relevant points that OTs should be aware of.
This document (see link) came out in 2011 on attendant services and sexuality and I thought you would find it useful ...(edited for brevity) But this document covers a real issue and is based on research in Sudbury and Toronto.