The only reason I wouldn't do something like that is if the came from different meters. I don't like having metering mixed, even if they are for the same customer. And seeing that they are from panels from different locations, I would probhably use striped wire for one. Just to make sure they don't get connected by the neutral by accident, although that would only be required if they were from different transformers, but still a wise idea.
Don't really understand why, the guy is doing it. Does this serve some purpose? Like say one was from a UPS, or generator.
