I found one sure way to make edge lighting work for everything..bear with me though. This is retarded and ultimately this is a broken feature on the Samsung S8.
Go to the play store and buy..yes, buy "Edge Lighting" by Edge Design. The free version won't work. You are welcome to test other edge apps but this is all that worked for me. Install the paid version of Edge Lighting and set it up by enabling notification access. From here, don't bother setting any settings up in the app, they don't work yet. Irony. Somehow, edge lighting kicks the Samsung lighting into gear even though neither app works by themselves yet. Now telegram, hangouts, calls, everything..works and shows the Samsung edge light. Face up, face down, screen on or off. It all works. Don't ask me why this works..I truly don't know. Let us know your results if you guys try this or other apps. Again, samsung needs to fix this. Its half baked because it doesn't even work with a full factory reset. I'm using verizon s8 btw. There is NO customization of colors yet. All notifications are a light blue for now. Nothing we can do about that yet.
Disclaimer: I absolutely promise I'm not trying to advertise their app or make them sales. I paid for this edge app and one other (purple app icon on the play store..I forget the name but it didn't work like this one did) for my S7 because I wanted edge lights for any app I wanted, and the color I wanted.