I've never filled it in electronically, but would assume you tick PPL(A) and fill in section 8 as appropriate. The Radio Licence is issued separately and runs as it's own thing, being renewed separate from the PPL(A) itself.
As for using US night flying time, the UK requirements are 3 hours dual, 1 hour dual cross country, 5 solo take offs and landings and 5 hours total night. You could use any US solo time to bump up the total time and for the solo requirement, but the 3 hours dual would have to be with a JAR instructor.