At the brewery I used to work for, we would dry hop certain beers, (like ESB, Pale Ale, and occasionally IPA) in the brite tanks, at around 38-40*. Always got a nice, clean flavor from them. I'm not sure if it diminishes the aroma, as I never had a control beer to compare it to. At home, I dryhop at the same temp as I ferment, or even a few degrees higher, and have had great results there too. Might have to split a batch and dryhop at different temps to see if there is truly a difference...