What’s acceptable format for submitting DVD master?

You can submit your master on DVD-R or DLT.  For dual layer DVD, it is safe to send DLT as it gives us a better control on where to set the layer break. 

If your DVD Video has any copy protection implemented then you must either send the image on DLT or upload DDP 2.0 image file to our FTP. DDP (Disc Description Protocol) is an image of the disc, essentially a “virtual disc”.  It eliminates the need for a DLT drive if you are planning to implement CSS, ACP or any other copy protection.