I don't know if you can do this on PC, but on the Terraria Mobile the Dryad sells Corrupt Seeds during a Blood Moon, even if the world has a Crimson Biome, meaning you can have both the Corruption and Crimson right next to each other.

If there's anyone out there who has done this, did you ever get some sort of feeling like you had just unleashed a great evil or something?

Yep