Realtors already know the price. It is Recorded in the Official Records and it's called a Mortgage. You might find it under the shortcut RM in the Court Clerks Website. You'll also find things like a Deed and Restrictive Covenants which you might want to study and disclose to the public if you're going to advertise in the MLS. What you're talking about is me going to a bank and telling them to settle a recorded mortgage and possibly a UCC for less than its legitimate securitized amount so you will know how to price a listing without being misleading.
Not true. Neither the mortgage nor the note, set the market price or the acceptable price by the lender in a short sale. I'm not about to do a short class on Short Sales on here tonight, but a short sale essentially means that the seller is selling for a price which will leave a deficiency, which the seller cannot pay, between the selling price and the amount owed on the note. Each lender is different regarding how much debt they will forgive, so NO, Realtors aren't privy to that information and thus they do not know the price which a lender will permit.
Regarding C&Rs, disclosure is not due at the time of the showing or advertising, so that is irrelevant. They are not required to be posted in order to enter a listing in the MLS.
A person making an offer on a short-sale listing is required to include a short sale disclosure to the contract, so disclosure is made that it will be contingent upon the lender approving it.