I think the premise of your question confuses considerations, unless I've misunderstood.
On all projects I own, the policy is that a bug fix will not be merged into a codebase without comprehensive unit testing demonstrating the case in which that bug was discovered, and that it has been resolved.
I do not understand why it matters _how_ the bug was discovered. If fuzz testing discovered that function foo throws tries to dereference a null pointer given input "ABABAB", then I would expect the engineer who chose to address that bug to investigate what property of "ABABAB" is the unaccounted for property, account for it, and then write a unit test calling foo with input "ABABAB", along with several other inputs that share the same discovered underlying property.
Fuzz testing may be a different method of testing, but the end result is, regardless, that you have discovered an input that your application hasn't been designed to handle properly and that needs to be demonstrably fixed, whatever it may be in particular.
On all projects I own, the policy is that a bug fix will not be merged into a codebase without comprehensive unit testing demonstrating the case in which that bug was discovered, and that it has been resolved.
I do not understand why it matters _how_ the bug was discovered. If fuzz testing discovered that function foo throws tries to dereference a null pointer given input "ABABAB", then I would expect the engineer who chose to address that bug to investigate what property of "ABABAB" is the unaccounted for property, account for it, and then write a unit test calling foo with input "ABABAB", along with several other inputs that share the same discovered underlying property.
Fuzz testing may be a different method of testing, but the end result is, regardless, that you have discovered an input that your application hasn't been designed to handle properly and that needs to be demonstrably fixed, whatever it may be in particular.