Frankly, if a rescue stick doesn't have btrfs-progs, it's not fit for purpose. A rescue stick should have the tools for every file system under the sun, because every file system is used by someone somewhere.
That said, I wouldn't generally use btrfs for a backup drive, because if you're using encrypting/deduplicating/integrity-checking backup software (you are, aren't you?) then you don't need any of btrfs' features.