My opinion: ceiling speakers and home theater should not be used in the same sentence; unless you the words "ceiling speakers" are followed by "should not be used in".
When you think about the principle theories underlying 5.1 and 7.1 systems, you will compromise the sound from your sides and rear by going to an in-ceiling design.
Now, if architectural circumstances are forcing you in the area, then there isn't much you can do. But if that isn't the only reason you are considering an in-ceiling speaker, then I would recommend going with dipoles/quadpoles for sides and rears.