I've seen players join alcatraz just to farm paint cans a number of times so I decided to try it myself. In about 1 hour I was able to collect over 300 paints cans (303 to be exact). It would take me about 7 minutes to run around the edge of the island and collect ~40 paint cans.
With this method you're able to grind dark matter in under 30 hours of gameplay, which in my opinion seems too easy. Not to mention you are also screwing your teammates over while doing this.