That's irrelevant.

Unless you own the receiving address, then you have no idea which wallet software the recipient is using. Even if the address was generated in Atomic wallet, there is nothing stopping the owner taking the seed phrase of the wallet or the private key of that address and importing it in to any other wallet software which does support spending unconfirmed outputs. Or even just creating a transaction manually and then importing the private key to a tool like coinb.in to sign it.