As somebody who is very keen on dominatrixes, I don't think a separate section is necessary.
For transgender, there is a clear distinction in service - they either are or aren't transgender.
For massage, the focus tends to be on proper massage parlours and services, even though they offer many sexual services, the section is quite distinct and worthwhile.
For domination, there is a lot of overlap, and a range from 'whore with a whip' to Dommes who don't even provide a sexual service, and you can get it at parlours, from indies, in dungeons etc.
I do sometimes search reviews for dominatrix, and there are quite a few search terms to go through (Mistress, domme, domination, BDSM, strapon etc.) so I could see that having it as a hyperlink category at the top (like sugar daddy) might be worthwhile, but not critical.