Have your agent ask the Listing agent if the seller is submitting one offer (yours) or is waiting, and submitting multiple offers to the Bank SS negotiator. Most banks only want to see one offer, but it is not always the highest offer. Many times Banks will accept and lower, ALL CASH offer with a shorter escrow because there is less that could go wrong.
If you have an open escrow then the Listing agent will be forced to change the status of the property to backup offers at minimum. If not the Listing agent will be violating MLS rules and will incur a fine.
As a buyer this is good in that it will cut down the possibility of competing offers that will distract the bank while working on this transaction. If escrow will open with no money, then you have an advantage. Just read through the escrow paperwork to make sure that you can walk with no fees anytime before the bank gives full approval.
What is concerning me, is why escrow is being opened. Usually escrow will not open until there is an approval. Right now, if this deal falls through, escrow is out some money. Not a lot, but whatever it takes for the paperwork, admin, etc. for it to be opened. Make sure the escrow company is okay with that.
Also, make sure your lender understands that you have made an offer on a short sale. Timing is key here. You need to work out an exact time line with your Realtor (he/she should be updated as to how and when the lender will approve the offer) and Lender (he/she should be keeping a close eye on rates). Locking a rate at a certain time will be beneficial.
Hope all goes well... Let me know if I can be of further assistance.