Actually, it's not without precedent. The Gambinos, under Paul Castellano, made an alliance with the Westies, who were nothing more than a street gang at the time--probably more drug-crazed and less organized than the Crips and the Bloods.
The story was that one of the Westies whacked a Gambino-connected loan shark over a $40k debt. Instead of avenging him, Castellano held a sit-down on their turf and, in effect, franchised them. That was one of many gaffes that pissed off Gambino capos and soldiers, and that assured that Gotti didn't have to answer for whacking him.