Wow, interesting questions. I appreciate your frankness in asking the question, and hope others will feel free to respond with their own thoughts.

My read on the situation is much like yours. That is, it seems absolutely appropriate and reasonable to mention the cerebral palsy for two simple reasons: first, because it represents a significant handicap that you have overcome (a positive!), and second, because it represents an important characteristic visible to the naked eye (a personal characteristic).

For similar reasons, I would suggest not mentioning the dissociative disorder. Although it may not have had an obvious impact on your academic success, most people will view this as a negative. Of course, it's an important characteristic that you have overcome just as surely as cerebral palsy, but I don't imagine that most folks will see it that way on the face of the matter.

It is of course true that the Psychology faculty represents a unique set of eyes, and that's where my analysis fails. Unfamiliar with the ideological and pedagogical standards of the field, I can't say whether a well-crafted essay remarking upon you DDNOS might not be a completely persuasive and compelling characteristic of your application. Others in the field and especially your advisers would best be able to guide you on this.

So at this point, I can only say that the safest course of action would be to eschew mention of the disorder. While you might hit a home run with it, swinging for the fences might well set you straight back to the dugout.