The only time that I have used the E-PL1 Audio to sync video clips, was with the Music video that I produced for my son. While shooting, I was recording the song track through the built-in mic, from an iPod running through a small set of speakers - that Ryan was lip syncing to - - - and then used the peaks on that E-PL1 audio to match up with the full resolution wav audio file that the many short video clips were being matched to. For the most part, I was successful in finding the matching wave pattern - - - and if I had taken more care with the way that the original audio got to the E-PL1, it would have been much better and even easier to sync:
So I'd think that if you were recording with both the E-PL1 and a Zoom recorder at the same time, that you should be able to match the 2 audio tracks after - for accurate enough sync. A definite advantage would be achieved by creating a noise with a sharp spike (like a clapper does) before recording each clip.