There is no IRS requirement difference between short sale and re

There is no IRS requirement difference between short sale and regular sale. As long as you have the binding contract signed before May 1 and settlement statement signed before July 1, you are eligible for the credit.
The problem is whether you can get the settlement statement before July 1 if it is a short sale. If the previous lender does not agree with the sell price that you and the seller agreed, a foreclosure process may be start. In that case, you may end up with invalidation of the contract.