DMC is set in the PRESENT. Castelvania has been set in different time periods...from past to the future.
The only thing remotely comparible is the gothic style setting....and thats it. Niether games PLAY the same OR have the same story/villain. Matter offact, there have been several different antagonists in the Castlevania series...DMC has maintanied the same one UNTIL this new one...which STILL has Dante in it.
So, again, i dont see the comparison.