Welcome. NEC violation, doubt it, if it is, it's a a minor/technical type rather than a 'you're going to kill someone/burn down the building' type.
As for OSHA, it may be more likely there, however as the article mentioned you can apply a variance if it is indeed a violation. Honestly, it's probably cheaper to get written up for it (if THAT ever happens) and then correct it within the allotted time.
There are probably millions of deadfronts with the old-style 'cam lock' fasteners that are broken/missing inoperable, most of which have been replaced with sheet metal screws in the corners. Not saying that is right either, just that it is prevalent.
If drilling a deadfront was never allowed, then all manual lock outs for breakers for generator feeds would be in violation.
and if it were me, I'd me more inclined to gig you for the missing hardware on the hasp or the open slots in the panel where the original lock went than the hasp itself,