This does nothing to the game itself AFAICT - i.e., if you choose a 16:9 (or 16:10) resolution, it will be stretched. Which means, OP is confused / wrong, there is no widescreen mod for this game (same can be already achieved with the vanilla game, if you really wish to play with a wrong aspect ratio, albeit with a lower resolution, by screwing around in your graphics driver and/or monitor settings).
However, that doesn't mean that the wrapper is not worthwhile! In addition to just running in a higher (4:3 - or other if you really want to) resolution, you also get the extra features mentioned by the OP! Nothing earth-shattering but still nice. (EDIT: I was confused myself a bit - the game is still rendered in the original 640x480 resolution, DXGL does nothing to change that. It just scales it with the improvements. It does not gain a lot in image qualit, but still noticeable)
Sometimes it can be used to bypass some Linux issues, too (via wine). Namely, in my case, NVidia has issues / hassles with providing pillarboxed modes (it can be done by the drivers, too, but that means editing x.org, and I had edited that feature away from my xorg.conf currently); and although some monitors can show 4:3 low-resolution modes correctly, some don't (as is my TVs case!)!
I read on the DXGL page that it can be used to bypass some bugs / incompatibilityes with older games and newer windows, and that was the motivation behind making it in the first place. I need to check this out with some other older games (I have had difficulties in running / and or crashing if I alt+tab, want to run in a window etc.) sometime later, too!
Post edited April 10, 2016 by Wild_Penquin