I can confirm that iDVD still burns DVDs from files exported from iMovie.
Steps I took:
1. Create a project in iMovie 10.0.1
2. Go to File>Share>File... and for Size choose Large 540P (960 x 540) and click Next
3. Choose a location on the hard drive to save the file to.
4. Wait for the blue circle activity indicator to finish.
5. In Finder, verify that iMovie created an MP4 file in the location specified in step 3.
6. Open iDVD and click "Create New Project."
7. Give the project a name and save it to your hard drive.
8. Drag the file you created earlier from the Finder into your iDVD project window.
(or go to File>Import>Video... and choose your video there)
9. Make any adjustments to drop zones, etc.
10. Click the burn button.
11. Insert a DVD and let it do its thing.
This produced a working DVD for me.
Here are my software specs:
OS X 10.9 Mavericks
iMovie 10.0.1
iDVD 7.1.2