If a goal of the RFE is to detect errors (e.g., if one node did not report back), a better way to address that would be out-of-band (e.g., throw an exception and/or pass an explicit error object).
Again, hook writers get the best of both worlds (with and without MOM names) if the design allows hook writers to decide. If hook writers want to have MOM names (and want to use them for some type of error detection), they can simply include them in the JSON output. If not, then they have the flexibility to create a uniform output regardless of the number of MOMs a job happens to be scheduled upon.