Using Lightroom as external editor for iPhoto, how to save image back to iPhoto
Unfortunately, I found several posts that explain why using LR as an external editor cannot be seamless (here's an example: http://forums.macrumors.com/showthread.php?t=1463251). This explanation makes sense to me for now. If I find something better I will update this reply. 

I don't shoot RAW all the time, so when I do here's my workflow:


Copy RAW files from card to desktop folder
Import (Add) to LR and edit
Export from LR to 'temp' desktop folder as JPEG files
Import JPEG files to iPhoto


** If I want to keep the original RAW files, I move the folder of originals, still on my desktop, to an external storage drive. If I don't need the originals, I can delete this folder.