Do I need a real estate agent to represent me in a short sale?
The simple answer to this question is going to be yes. A short sale involves lender approval and I do not know a single lender that will allow a buyer to represent themselves in a short sale, the liability is simply to high. A real estate agent is licensed and understands the process, required disclosures, has marketing tools available (MLS and lock boxes), and will have the know how necessary to deal with bank asset managers, and others that will inevitably become involved in the transaction.
Bottom line, the bank is not happy to be involved with a short sale, if it is to go through, they will ensure it is done professionally and efficiently - two things that a novice cannot offer. Unfortunately a short sale is no place for a crash course in "for sale by owner" tactics, and the lender is not going to hold the hand of anybody when listing and negotiating a short sale.
Find an experienced short sale agent, and accept their professional expertise as necessary.