Just tried a couple of export options from a short film made with iMovie10:
SD, 540P and 720P exported them as a seperate file (mp4) no problems in dragging them into an open iDvD window. They render fine,
However when trying to use the media button in iDvD and chosse either foto or film iDvD will crash, however using audio and within iTunes directory pick "film" the films I shared thrue iTunes are available , can be dragged and render fine.
Clearly iDvD is abandonde already for a couple of years now, but still can be used .