It depends on the drugs. There are a lot of cases of producers selling on these market places. Look at a lot of the marijuana vendors, the vetted LSD vendors, the mushroom vendors, etc. Beyond that, there is violence involved in later steps of the drug trade: smuggling, gang turf wars.
There are problems with some of the manufacture of cannabis. Criminal gangs use trafficked workers, forcing them to work in cannabis farms.
If I was a criminal gang using slaves to grow cannabis I think I'd market it as some home grown organic low yield crop with images of open fields and nice trees.
Maybe in Mexico they do this. Here there are investors who buy up a dozen houses through shell corps and hire one grower who sets everything up, and is paid a lot of money. The grower then hires people to maintain and protect the grow usually for pretty good money as well. http://www.cannabisculture.com/articles/3268.html
