In a nutshell, no. Brad Feld, a well known entrepreneur, author, blogger and venture capitalist in Boulder, Colorado who wrote a book called "Venture Deals: Be Smarter Than Your Lawyer and Venture Capitalist", wrote a great blog post in 2006 explaining this situation. He has a quote from Guy Kawasaki on why VCs do not sign NDAs. The entire blog post is worth a read.
“Before you even start addressing the hard stuff, never ask a venture capitalist to sign a non-disclosure agreement (NDA). They never do. This is because at any given moment, they are looking at three or four similar deals. They’re not about to create legal issues because they sign a NDA and then fund another, similar company–thereby making the paranoid entrepreneur believe the venture capitalist stole his idea. If you even ask them to sign one, you might as well tattoo “I’m clueless!” on your forehead.”
Mark Suster, another well known entrepreneur and blogger turned venture capitalist, has an equally great blog post on the topic that goes into more detail on confidentiality above and beyond NDAs.