Funny things happen when conduits aren't sealed. Condensation will accululate in fixtures and conduits. Althought the fixtures and conduits may be rain-tight, or vapor proof, unless you stuff some duct-seal in the conduit, it will act as a vapor path outside the fridge. That cold air will mix with the warm air outside, and then you get a micro-weather system inside the conduit.
Mark Heller "Well - I oughta....." -Jackie Gleason
Equipment must be suitable for it's location- and that, of course, isn't always clear. Thinking back, it seems to me that every freezer/ walk-in that I've been in has shared a few construction details. While the boxes near the fan were of the "usual" type, the light switch, when inside the unit, has been of the lever-operated weatherproof type. I think that this is am attempt to comply with NEMA standards for equipment that will operate even where there is external icing (Is that Nema-3S?) Lights have always been enclosed- either incandescents inside "jelly jars" or fluorescent tubes inside plastic sleeves. Wiring has always either been pipe or MC.
I can't say any of this is "required," but it does seem to be the practice. Where the freezer is used for food, the USDA and the Commerce Department (fish) have a slew of their own regulations as well. I am sure the NSF (National Sanitary Foundation) has a standard that applies.