[NAME], The probe actually allows either 1 or 0. The rest of the return  type means the probe did not receive what it expected to receive thus the failed notification. The 1 and 0 are just indications that backup is not required  and thus logic should be controlled by the script on the client that the probe is going to initiate. A failure means that things aren't going as you intend it to but a return of 1 and 0 is intended to control if a backup is required or not and thus is not actually a failure and thus marked as successful. This makes more sense when you have a automated ticketing system which created incident tickets automatically on failed jobs.
According to the Networker documentation, when there is a probe action in a workflow, only is the return code of 0 from the execution of the probe script considered as probe check success, and the following other (backup or clone) actions will be executed. In Monitoring window of Networker Administration, the probe action would be marked with a green check if the probe script returns 0. When the execution of the probe script returns other codes like 3, 7 or -3, the probe action would be marked with a red cross in the Monitoring window, and the following actions would not be executed. The only exception is when the return code is 1. In that case, the probe action is marked with a green check, looks like a successful probe check; but the following actions in the workflow would not be executed because the return code of 1 means a probe check failure. Why the return code of 1 from the probe script is marked with a green check in the Monitoring windows? Is this done on purpose or a possible display bug? I found this issue in both Networker 18.2 and 19.1.
A possible monitoring display bug for Probe action check result in Networker?