It should come off without any major problems.
If the angles are too steep, lets say over 90 degrees, you might have to soften the normals on your low poly mesh.
It also depends on how much the models differ from each other. If you added a major extrusion, the normals will be hard pressed to display hard angles.
What package are you using to perform the high to low poly conversion?
Hope that steers you in the right direction.
Post some screens of the models that are causing you trouble.