I don't have ALL the details, but the files in question do contain info regarding DVD chapter points that you may have made in Premiere. In Encore, you can use "Import As > Timeline" and just select the audio and video clips at once, and Encore will just know to use the other files and will import the chapter marks into the Encore timeline.
There is no harm in deleting those files, other than potentially losing the chapter info. All you really need to create a DVD in Encore is the video and audio clips, typically .m2v and .wav to be precise.
Once I create a DVD and I'm happy with it AND the customer is happy, I delete the .m2v and .wav files. Note that when making a DVD, I create a "Disk Image" or .iso file from Encore. THAT is what I keep as a Master - most any DVD burning software can burn a DVD from that .iso file. I use the free ImageBurn for that, so I never even need to open Encore to make more copies. In fact, the Encore project could also be deleted at that point once I have the .iso, keeping in mind then that no further changes could be made to the DVD later.