If it supports backup to a file, you can have it write to a named pipe and from there to wherever.

I used this hack for backing up Oracle 30 years ago.

Something like 'mknod p backup.dmp; oradump .... file=backup; dd if=backup.dmp | ssh othermachine receiver-process'

Not necessarily. That won't work if the backup uses apis that a pipe doesn't support, like seek or reading back from the file.

Sure; does any backup actually do that? I guess it's possible.

Backups (at least db backups) used to be made with the assumption that the backup device is tape.