How many psychologists/philosophers suffered from a mental disorder?

Not all of them, though I was tempted to suggest the opposite ... ;)

I'll amend that:  only the really good ones ... ;)

"How many psychologists/philosophers suffered from a mental disorder?"
This is a rather open ended and absurd question. Are you asking about
famous philosophers? Generally, "psychologists" are licensed by state
agencies.
It is well known that many famous writers and composers tended to be
manic/depressives.

I think it is a good question. 
Consider the following view by Daniel Nettle:

"Strong Imagination: Madness, Creativity and Human Nature"
Product Details: 
ISBN: 0198507062 
Format: Hardcover, 235pp 
Pub. Date: March 2001 
Publisher: Oxford University Press 


http://search.barnesandnoble.com/booksearch/isbnInquiry.asp?endeca=1&isbn=0198507062&itm=6

I read something in th last few months about a UK study of psychiatrists.
Important note: Psychiatrists have to qualify as medical doctors
first, while psychologists are PhDs that skip the fluff and get right
down to brass tacks.

In any case, this recent study of UK *psychiatrists* reported that
these folks had *higher* incidence rates of mental illness than the
general UK population.

Efforts to understand Creativity have drawn links with some mental
conditions, disorders.  An article by ulrich Kraft, "Unleashing
Creativty", on page 16 of the Scientific American "Mind" 2005-APR
special issue may assist you in your research.

http://www.sciammind.com/issue.cfm

Hmmm?  I thought that I had posted a comment suggesting that
philosphers should be included in the discussion, Nietzsche, et al.,
but maybe one of them was offended.

Not that either Psy or Pho has to be a genius, there is the theory
that genius is just this side of "mental disorder".  Maybe the
"shrinks" get infected by the people they deal with (grthumungous's UK
reference, or maybe they as professionals just recognize and admit to
the symptoms more quickly than the general public.

Are you asking about the exact number of philosophers and
psychologists in the past have suffered from mental disorders?  If so
I don't think there is a documented answer anywhere.