I think that we ought to accept what people inthis thread (and elsewhere on cd.com) who self-identify as fetish dressers have said. They have largely said that unlike identity dressers and TS folk, they don't dress because they "want to be a woman" and that they don't self-identify as a woman.
I cannot say whether this is true of all fetish dressers, but it does seem to be the prevailing sentiment on cd.com amongst this section of our community.
I can, however, say with a reasonable amount of certainty that there is no sexual stimulation element in a TS person's need to express their brain gender. Speaking purely personally, I know that my need for sexual release is much lower when I am presenting as my brain gender than when I was trying to portray a man.