I beleive the VCAP is an open book exam. For the VCAP-DCA they provide the PDF's
For VCAP-DCA you have access to vSphere documentation but if I remember correctly there is not this possibility on VCAP-DCD. Btw that's make sense because DCD is about designing vSphere based on specific requirements. You don't need docs for such work as it is more about principles and methodology which is not quickly searchable on any doc.
For the VCAP5-DCA, you have some of the documentation listed in the following thread > Re: Materials available during VCAP-DCA exam
When I took the DCA, only 5-6 of the above listed pdf's were available. It doesnt matter really, because if you have to look up the pdf's more than once/twice - you havent prepared well enough. Time is VERY limited for all VCAP exams.
For the DCD - there is NO documentation available. My experience is here http://virtualizati0n.wordpress.com/
Good luck with whichever VCAP you decide to take!