Luther was not, however, he was working for the government in order to gain some form of early release…till he tried to kill superman for the umpteenth time. however, he also helped with task force x in some capacity in the Justice League cartoons, likey being the one to make the ceramic guns used by Deadshot when they invaded the watchtower.
The wall does not ask you to join task force x the wall implants you with a explosive and tells you your now going to work off your dept to society or she blows your head off. which is the point of recruiting the Joker as would not take the deal, thus would end up like KGBeast did in Batman: Assault on Arkham (Movie) thus no more joker. joker takes the deal, she still ends him to show that the bombs are real…because he beat a puppy to death with a kitten and The Wall loves kittens. sorry could not resist a joke after my new kitten just squeaked cutely in her sleep.
On a alternate but related note: why has batman not said a four letter word it and thrown joker into the Phantom zone.
if i remember correctly during the red king storyline in jl:classified. They showed a timeline in where earth was going to blow up so the jl moved to a new world but they send every prisoner to the phantom zone(They specifically showed Batman villains) but in canon I have no idea.