I can confirm that LR 2015.3 on Win7 does not show the preview for LG G4 DNG files in the Import dialog.
The Library does show the thumbnail fine as well as the zoom-in loupe.
The Develop module shows it fine.
Given that ACDsee Ultimate 8 does not show the DNG contents at all, my first guess is that the G4 DNG files do not contain a JPG preview and that the import dialog displays only the JPG preview from the files.
i use win 10. the lg has a jpg as well. actually, if i import with Airmore app i can see the preview. after i import to my hard disk, the LR dose show the preview on the import dialog. that's make the whole process long and complicated.
For me, I need to manually copy the images to my hard drive first then import from the hard drive because LR wants to load every image file found on the phone into the import dialog.