Being as I put my foot in my mouth a few posts back I'll take a stab at this. Db minor is what I would consider a theoretical key you might discuss in a classroom, but would probably not see in the "wild." It would occur naturally in a modulation from one flat key to another, but for ease of reading and comprehension you would write it as C# minor.
The only way I would expect to see Db minor would be with a composer who used it as a matter of artistic license

. Perhaps there are other legit reasons, but I can't think of any.
Hopefully I got it right this time

.