A hacked server can have the backup server pull false backups as well.
Of course, your servers shouldn't be SSHing to your backup servers, but that goes both ways.
If the backup machine is compromised the attacker can corrupt your backups. Either way, if machine is hacked you risk loss.
Of course, this is an edge case, but I believe setting up a pull-based backup system is still going to be less work than a write-only push system.