You would think the simple answer would be no. However, when it comes to REOs, nothing is ever simple. The banks have stacked the laws in their favor over many years, and when the law is not in the banks favor they might ignore it or violate it anyway.

So lets say buyer PK went into contract with Downey Savings on one of their Repo's -
The FDIC shut Downey down and moved the assets (including the house that PK is trying to buy) into a legal limbo. - Downey no longer owns it, the Federal government does - sort of. But the Feds might not want to actually transfer the title into the FDIC name so the county still shows Downey as the title holder, even though they can't do squat with the property.
In the interests of the community, the financial system, FDIC, and PK, it does not make sense for this house to stay in limbo for months when there is a ready and willing buyer. So, with a little hocus pocus the contract you have with Downey is magically changed to a contract with "seller of record"
- Despite the fact that you made a contract with Downey, you now have a contract with an apparition.

Oh, you asked if this is LEGALLY enforceable. You know, legal questions can only be answered by lawyers. So this is not one of those lawyer type answers.

I have never seen a seller of any type - lender, shmender, builder, force a buyer to complete their purchase. Have never even heard of it. Oh, if the seller has fully performed, and the buyer has no unreleased contingencies, a seller can demand to keep the buyers deposit for damages. But the seller can't force the buyer to complete the sale.

If the seller(s) of record has performed the sellers obligations under the contract and the buyer has released all of their contingencies, I don't see why the contract couldn't just proceed to close escrow as scheduled. It is not like a personal services contract where you care if it is Bruce Springsteen or Bruce Willis performing rock music at your kids Bar Mitzvah.

It should not matter to the buyer who signs the deed. It could be some clerk from Downey, FDIC, Wamu or Shamu. - Who cares? It is just some anonymous clerk signing the deed.

So without legal advise here - No, it should not matter who is selling it to you. It is the terms and conditions of the sale that matter.

the property is called a "REO" -- an expression which means "real estate owned" by the lender. so lender would own title.
contract is legally binding an can be enforced-

you should seek legal advice to proceed further
good luck

A real estate sales contract (or often called purchase agreement) is a legally binding contract that holds every party accountable for the smallest detail

need more info to answer question