If exclusively breast fed, is it ok for a baby to be given a pacifier in the night?

Yes. Although there are breastfeeding advocates that would disagree, pacifiers do not confuse a breastfeeding baby. You do not want to substitute the pacifier for nursing, but its use is fine between feeds, and especially at night.
Yes...but. The kid who develops a need for the pacifier to fall asleep will eventually loose it in the night & cry until you come back in and re-insert it. If you want to get up to do this every hour or two all night go ahead. Sometimes it is best for them to learn to settle without any crutch. If they are older & can reach around & find it for themselves there is no problem.
Paci and breastfeed. Yes no problem that I have ever seen for breasted babies and pacifiers.