DoF will most likely come out at least 5-6 months before SC2 (if it comes out in early 2010). DoF is fantasy, while SC2 is sci fi. Dof is an mmorts. DoF has giant fancy fortresses and castles. So while they are different, there will be a little bit friction between them I would say.
Picture made by Aametherar the orc (Elves are the best!)