Transfer Video to iOS iMovie
Bare in mind only footage shot with an iDevice can be edited on iMovie for iPad. That being the case, it's just a matter of finding the correct format.

Wired has dedicated a whole article to this specific matter.
Basically it comes down to convert the video to a specific MP4 with the H.264 codec. You can do this by following these easy steps.


Convert your movie to .mp4 on your Mac (if it isn't already in this format)
Convert your movie to an iMovie movie with the 264 codec
Use iTunes to transfer you movies to your iPad


Normally your files should appear in the iMovie project dashboard.