Currently the only X1 box that can do 4K HDR is the DVR XG1v4. I have not read anywhere about that box having the ability to do Dolby Vision. For live streaming from the Olympics I would suspect NBC would employ the HLG form of HDR.From what I was told by my old TV Broadcast buddies the UHD/HDR is a NBC/Comcast exclusive. Not sure this is correct, but they also tell me Comcast's X1 STB is Dolby Vision capable over the HDMI output and the broadcast includes the DV sub carrier.
Here is the link to the events that are being shown on Channel 106/DirecTV.Channel 106 on DirecTV will be showing the Olympics too in 4K/HDR.