How many gang members are working for the FBI, DEA, BATF? Probably most of them.
In this case, it sounds like they were mostly a prison gang. Actually, most white power/nazi gangs are prison based. Such prison based gangs always have a non-prison side, and RICO is the right tool to go after them. But you are right that they probably flipped one of the members as an informant, and that's a good thing (in this case). Unlike the "Whittmer kidnapping" setup, this looks to be a legit operation.