FBinNy is correct. The small amount of bending in that dropout would not cause a crack in a previously-sound dropout. If there is a crack in the dropout it was probably due to some previous mishap. That dropout appears to be chromed and then painted over. Chrome can crack pretty easily when the metal beneath it is bent, as the chrome is quite brittle. A nice gentle way to open the dropout back up again is with a large cold chisel. Insert the tapered end of the chisel into the "mouth" of the dropout. Tap gently. The taper will slowly wedge it open. Stop tapping when the opening is back to where it should be. Do be carefull to use a large enough cold chisel that the cutting end never touches the steel of the dropout: You are using the chisel as a wedge, not as a chisel.
Brent