those black body radiators(doesnt exist) will be visible in the IR...unless you can get them down to 3K to blend in with the background. Running a spacecraft that cold is pretty impractical because all the bus equipment uses power and any power=heat. Any power generation will be hot, rtg or solar.
"A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence." [0] Black bodies are theoretical, they do not exist. Apollo had radiators, they might have been black but they were not a black body. Vantablack comes close to a black body for the visible spectrum which is p cool tho.
yes that is more parsimonious however in non-technical language the term "radiator" is associated with heat exchangers. if you put heat exchangers on the sides of your spacecraft they would function as radiators so I suppose it doesn't matter anyway, arguing semantics is a waste of time.