The FARs still allow supervised PIC to count towards the PIC required for an ATP. It looks black and whote to me.
Technically, Feds and DPEs should be onboard with the concept but it's so rare I wouldn't bet on it...or show up for a checkride expecting them to just "be good with it".
For either a 91 checkride, or an airline checkride, let them know well in advance that you plan to count this kind of time, and let them know how it's documented. That will give them the time to get educated and get back to you if they have any concerns...sort it all out before the checkride (91) or starting class (121).