They definitely are. Drugs are not teleported to American consumers when they reach the border, there has to be an equally corrupt distribution structure in the American side, and that only works involving corrupt officers. A lot of money attracts a lot of scum, as we say in Mexico, "con dinero baila el perro".

There have been instances of law enforcement trafficking arms to the cartels, because "we're going to track the arms and arrest them": https://en.wikipedia.org/wiki/ATF_gunwalking_scandal