Gfretwell: 525, dealing with carnivals and similar functions, is a fair section to reference. I think your citations of 525.22 and 525.23 are quite proper, and more appropriate than just the catch-all category of 'temporary installations,' Asticle 590.
That said, it appears to me that this assembly can certainly qualify. Mounted on the same board as it is, I think we have to interpret 'within the box' requirement of 535.24 to have been met; we certainly apply that standard to main disconnect / gutter / meter-main assemblies.
n1ist, I wouldn't doubt that everything is connected with chase nipples. I might even accept simple plastic bushings, as long as some means is used to ensure grounding continuity.
When I come across such a construction - or, when I make one myself - I ask whether I think the thing would meet the requirements a commercial product would have to meet. I'm willing to cut the maker some slack; for example, the DIY 'extansion cord light fixture' featured elsewhere on this forum lacks a sticker specifying the largest wattage lamp, and I would not hold that against a guy in the field.
The next question is whether the item is appropriate for the circumstances. Again, as an example, commercially made 'spider boxes' are made for use in wet locations, while this assembly is not. Is it in a wet location? If not, I see no need for it to meet those requirements.
The final factor ought to apply equally to all items, whether DIY or factory made: Maintenance.
In the debate of DIY cords, many photos were posted of damaged assemblies, often missing parts. That's not fair; anything can be broken. If the equipment is damaged or incomplete, it needs to be taken out of service, regardless of whether or not it has a "UL sticker."
