I think it means that strong, violent dope-pushers who are making lots of money are doing it by selling drugs to "fiends", or addicts. As in many rap tunes, the lines seem to be created as much for rhyme as for meaning. I'll assume you know that this kind of language is African-American dialect and isn't the standard English taught in school.
I think, in this lyric about the state of California, that particular line refers to several things he has already mentioned: the music industry; the extensive marijuana-farming industry; hookers bringing in money for pimps; and so on. I think that in this lyric, he's viewing the entire state as a "money-making machine".
In addition, it's a take-off on an advertising slogan for the George Foreman brand of counter-top kitchen grills. They are widely advertised in the U.S. as "lean, mean grilling machines." Most Americans have heard or seen this phrase in that context.