I've got a wired issue going on.
I have a project in Apple prores 422 HQ 25p 1920x1080 with a track dedicated to titles with video files in 25p 1920x1080 animation codec in RGB+Alpha.
My titles suffer from a loss of quality around the edges and became rougher and slightly pixilated once in Final Cut 7. However the original export in Animation RGB+Alpha is fine.
Here are screen shots
Here is a text plate screen shot. Done with MPEG streamclip (to avoid going into FCP7 who could change anything) from the original Animation RGB + Alpha video file that I exported from After Effects. Everything looks perfect: http://imageshack.com/a/img674/5470/KC9tyq.jpg
Here is a screen shot from FCP7 with the text in the timeline over an image. You can see that the edges are now ruff. It is the same issue if I open the file in the FCP viewer so it should not be a sequence settings issue http://imageshack.com/a/img538/9139/fpfLid.jpg
I then exported an Apple Prores 422 HQ version of the video file from After Effects. I brought it in FCP7 and put it in the timeline and exported a video test and it looks good. Here is a screenshot. It looks perfect, no roughness on the edges http://imageshack.com/a/img674/5470/KC9tyq.jpg
My conclusion is that there is an issue with FCP7 dealing with the animation RGB+Alpha video. My issue is that I need that format in order to get the text in overlay over my main video track.