I would not advise putting in a contingency offer on a short sale.
- First of all it will probably be rejected. They want to sell the house now, and don't want to wait to see if yours will sell.
- The lender will take all the offers they can get and accept the best.
- It takes a long time to get a response from the bank. You may be waiting 8 weeks before having your offer rejected.
And remember that you buy a short sale AS IS. They will not make any repairs.
Be sure you know what you're doing, or work with a realtor when dealing with a short sale.