Keep a look out for these in the near future, wouldn't pay to bump in to one. Hopefully they work and start removing the masses of plastic and we get to see the difference in our lifetime.
This is what I found on their website about preventing collisions with their system:
But, in the event that a vessel does pass through the patch, we have implemented extensive measures to ensure the safety of both vessels and our cleanup systems. Each system will be equipped with lanterns, radar reflectors, navigational signals, GPS and anti-collision beacons.
The AIS will continuously broadcast the location of the systems to passing vessels and the GPS will track the location of our systems, should they veer out of the patch. The US Coast Guard will chart the area as a special operations zone and will issue a Notice to Mariners concerning the presence of our systems.
If with all that, and you still manage to hit one, then you must have been doing something very wrong ;-) They will certainly be one to watch.