Kevin, you will NOT see a vid clip imported via iTunes in Camera Roll OR Videos - the ONLY place you will see it is AFTER you have launched your iMovie project and are inserting video clips...the clip will appear there along with existing Camera Roll media.
So an option is to create an iMovie project and import only that clip you got in via iTune then save THAT project as a movie to your camera roll. Then it will be there forever and ever.
Go back to iTunes on Mac/PC and dump the vid from iTunes so it does not sync back into your iOS again to save memory there.
Also, iMovie on iPhone has cool but limited titling. I used a drawing app on my mac to create a 640x480 graphic–black with white text with url, etc. and shot a still and a 2 second vid clip for using in the output.
Sound volume is a problem, will be using a bluetooth mic soon. Here's a vid.
http://www.youtube.com/watch?v=ELk-VrSRg5A&list=UUJmXMGv7HkwTZuaMTBz9cRQ&index=1 &feature=plcp
I have a few more in "preproduction" : )