WordNet sense 1 (someone who works (or provides workers) during a strike):

scab, strikebreaker, blackleg

WordNet sense 2 (a person who is deemed to be despicable or contemptible):

bum, crumb, lowlife, puke, skunk, so-and-so, stinker, git, rotter, stinkpot, dirty dog

WordNet sense 3 (one who reveals confidential information in return for money):

betrayer, blabber, informer, squealer

WordNet sense 4 (take the place of work of someone on strike):

fink

WordNet sense 5 (give away information about somebody):

betray, denounce, grass, shit, shop, snitch, stag, give away, tell on