Mind reading is always a challenge ...
I see the reference to a cover as simply the code panel not able to imagine something weatherproof without a cover. A similar assumption, I believe, is behind the code language about 'in use' covers.
The NEMA test methods date well back before the 70's. I remember them, being discussed within UL in the mid-60's. They were always independent of UL; that discussion is ultimately more about internal politics and marketing than anything else.
Nonetheless, The NEMA enclosure standards in no place even mention covers. All that is required is that a complete product, installed properly, pass certain performance standards. In the instance of NEMA-3R, the crucial test is a simulated rain at a slight angle.
If you look at some "outdoor" cover plates - designs pre-dating the 'in-use' designs - you will find a short hood projecting over the top face. This lip was clearly designed around the NEMA rain test; that lip is no wider than required by the slant of the 'rain.'
When a question arises, such as the one posed by this thread, I ask myself: what would happen if we did the industry-standard tests? Knowing the standard and test procedures, I opine that the fixture described would pass the NEMA -3R test quite handily.
Another thread active today discusses devices wired without the bother of using a box in the wall. One must be careful; not to assume that 'different' is 'wrong.'
