2013 MBP Hotspots in Backlight / Apple Warranty
1) I haven't seen many reports of flat spots like this over the past few refreshes of the MacBook Pro so I wouldn't consider it a widespread or known issue.  Only Apple will know for sure, and if it is then they would likely consider a Repair Extension Program (REP) to handle repairs for these symptoms outside of the 1 year warranty.  Only time will tell.

2) I would expect Apple to cover this so long as theres no signs of damage or trauma to the MacBook Pro.  AppleCare provides an extended warranty for failures and defects that are not a result of accidental damage. Ultimately it depends on the human being you end up dealing with but if I were you I wouldn't expect much pushback on having it repaired.