Not Zedd and Skrillex. Grey sent the Where Are U Now remix to Skrillex, who sent it to Zedd, who became a fan.
Very sure it's Singularity. I've done some research, and Singularity's music has a lot of subtle sounds in there that sound identical to some of Grey's sounds, especially the guitars, hats, and some bass patches especially in the Same Old Love remix. Both live in LA, Singularity reposts all the Grey stuff, and some guy on Reddit mentioned that he's friends with half of Grey, and that this person is an alumnus at Insomniac's EDC Discovery project, which Singularity also happens to be a part of. GetYourSnackOn co-owns Singular Sounds with Singularity, and his Twitter account (@tnorris) is full of Grey reposts. GetYourSnackOn makes frighteningly accurate remakes of EDM songs, and that future bass sample pack (which I have) contains a synth preset that was used in the Papercut remix