Are you sure that Open GL is necessary to build a 2D tile engine ??? I think libraries like SDL (http://www.libsdl.org) are much faster in that case... Or maybe you have some special goals that force you to use Open GL (for example performing 3D rotation to your BG). Open GL is good for 3D development. But for 2D... I really dunno.
I have a 50% complete OpenGL-based tile engine, using triangle strips for the tiles. OpenGL can do a whole lot more effects than DirectDraw. You can even simulate Mode7 pseudo-3d graphics, SNES-style. I think OpenGL is the way to go, as long as you make sure that any you don''t get any unnecessary bottlenecks.