In the US you can both log PIC when practicing Instrument flying, one under the hood and one safety pilot. But you both have to be rated on the type of aircraft. For example, if you have no 'night rating' and you're flying under the hood with a safety pilot who is night rated, at night, then technically you cannot claim PIC for the flight!
Don't think so. Read the FARS all in part 61.51 e
--they allow loging as PIC when [1.i] "sole manipulator of the controls" and when rated [in category and class]. There is no mention of flight conditions.
Thus a PP without an IR can log PIC when sole manipulator in IMC, a PP without a complex or HP endorsement can log PIC when flying a complex/HP plane, and a brit whose license is restricted to day only can log nighttime (he is rated in category and class, but not the flight conditions).
what these people cannot do is ACT as PIC. There must be an appropriately rated person who can act as PIC and who is legally responsible for the flight.
Now--can that person acting as PIC (who is a required crew member) also log PIC? It depends--The FARS allow the person acting as PIC to log it only if
[1(iii)] more that one pilot is required under the type certificate or under the regulations under which the flight is being conducted.
thus in the simulated instrument example, YES, since it requires a pilot and a safety pilot. In the night example [without the hood] no, since night flying does not require 2 pilots. In the night example with the hood, the fact that the person who is sole manipulator is not legally allowed to ACT as PIC should not prevent him from logging it under [1(i)].
-m