Worked with it this morning. You can add photos and videos to your Camera Roll as well. The trick is you have to rebuild the Camera Roll database to make them visible though.
Using the File System viewer in the PhotoData folder, delete the Photos.sqlite files. Disconnect and reboot the phone. Open up the Images app and your Camera Roll will now be blank. But be patient and it will rebuild the database with the new images/videos (your albums should also be intact).
If you don't force it to rebuild the databse you can copy over stuff but your phone will never see it.
Finally got a Honeymooners episode from my DVR to my Mac to my iPhone and this last bit was part of the process. Now that I know how to do it, it's a matter of streamlining the process. Unintuitively, it turns out that video recorded by your phone is stored in the Camera Roll. That means within the file system it's stored in the DCIM folder. I'm not sure it matters, but I followed the naming convention I found there for my video.
Not sure where "actual" video (i.e., video you can see via the Videos app) is stored, nor if anything placed there other than actual purchases or downloads would show up.
I'm guessing you can get ringtones in somehow as well, but I've only glanced at that right now.
