The original nitride hardening treatment extends deep enough into the surface of the journals that a minor cut doesn't usually remove it all, -but the hardening rapidly weakens the farther into the surface you cut. Running a cut crank certainly isn't ideal but there are some who have done it without issue. I won't recommend it.
The good news is that some nitride hardening processes
can be repeated on the same part in order to restore or even further strengthen the treated surfaces.
The bad news is it's almost impossible to find someone willing to perform this process for you, and if you do it won't be worth it when you can just buy a good uncut used crank for $150.
Looks like you got a really big paperweight or a really small boat anchor on your hands.