here is a thread I came across before - dosing pumps to feed seahorses
http://www.nano-reef.com/topic/307716-automatic-feeder-for-nps/
my gut feel is that you run the risk of clogging the line due to size of the shrimps.
As for shelf live - they say you can keep commercially frozen fish for upward to a year - shrimp 6-8 past its printed sell by date (and this is for human consumption). So i'm guessing upwards of 8 months.