Well look. It's a federal crime to buy, sell, or possess pot. Unlike the CIA, whose mission is to break (foreign) laws, the FBI's mission is to enforce US laws. How can you hire a federal law enforcement officer who is also a scofflaw? Very problematic. The solution is probably to use some sort of contractor classification to hire hackers indirectly. Obviously the FBI has no problem working with confidential informants who are criminals of the worst sort. So probably a white hat hacker who partakes in the weed is not that difficult to reconcile with policy, as long as that person is not an actual agent.