If the ATO/FE occupies a control seat, they are the PIC. The ATO/FE cannot be the PIC from a jump or observer seat.
61.095 defines ICUS, and a flight test meets the requirements, providing the pilot is already licensed.
Dual for RPLs, or any other licence test if it is the pilot's first licence. All other flight tests are ICUS.
The FEH stupidly requires applicants log dual for all tests, but flight tests are not flight training under 141.015 or 142.015, nor under any other rule.
61.345 (3)(f) lists the 4 types of flight time activity that must be logged: PIC, ICUS, co-pilot and receiving flying training (dual). The RPL is not flying training so shouldn't be dual, can't be ICUS because the pilot isn't licensed yet, only leaving co-pilot. This result would look a little weird, and I can see why dual is preferred. I wish there were more simple guidance that actually complied with the legislation.
There's no requirement under part 61 for an ICUS logger to be recent or current.