Interestingly, I am pretty sure (from both US instructors & reading the relevant FAR part 61 notes) that my FAA PPL issued under Part 61.75 on the basis of my JAR PPL does allow me to fly with passengers at night providing the currency requirements are met.
No it does not. Read the bit where it says:
"ALL limitations and restrictions on the United Kingdom Pilot Licence apply"
If you do not have a night qualification then you don't magically get one under a part 61.75.
Your UK licence requires an entry on page 3 that says "the privileges of this licence may be excercised at night" without it you are restricted to DAY/VFR and thus the paragraph above applies.