1. Nec based Optiarcs are better readers and I think that's why they show more green than the red stuff with Lite-Ons. Just look at the posted scans in this post.
2. The DRU
3. If it was a DVD Video you should see some disturb ions while you watch the movie at that spot.
4. I would burn a regular SL Verbatim disc to find out how such a scan looks
This disc was burned with my Optiarc 7200 and gave these results if I scan with my Lite-On or the Optiarc 7200. (My 7240 is currently removed from the computer).