it wont affect their dreams. they will wake up sooner than if they weren't dosed, and will wake up tripping. that is all.
ive fallen asleep while coming down on LSD, and even that is hard to accomplish. the reason you cannot sleep on LSD is because as well as being a hallucinogen it also works as a stimulant on your central nervous system. its like trying to sleep on speed.
ive also dosed someone with LSD while they were asleep after they requested it. they did not dream. as far as i know, most people don't seem to dream if they're asleep with LSD in their system.
if you want crazy dreams, take melatonin.
if you want to trip balls, take LSD.
btw - you probably could've googled this.. :/