I like to have graphics rendered to the codec and frame size that I’m finishing in. That way, I don’t have to render the material again. This works unless you need an alpha channel.
So what codec are you going to be finishing in? Let’s say it was 8-bit uncompressed in anamorphic 16:9. That frame size is 720×480 and then FCP stretches it to display as 16:9. I would have the animator render out the animation as 720×480 in the Apple 8-bit uncompressed codec. I would bring it into FCP, select the anamorphic check box in the anamorphic column in the browser, then drop it in the sequence.
-Russ