So the diplomacy expansion allows players and AI to offer pirates missions... I tried this out and it didn't work to well.
I offered the pirates 13k cash to form a 'massive' fleet made up of 300 or so pirates against a specific AI's planet. After I clicked "make offer", it took me back to the pirates page and when I moused over the pending offer I noticed the planet I targeted was wrong, about 8 jumps wrong. Also I saw a small fleet consisting of 40-50 pirates max assault the first planet of the AI I targeted and that wasn't even the planet I specified or it wrongly targeted.
There was no confirmation the offer had been accepted but my money disappeared and there was no 'massive' fleet attacking the AI i targeted at all.
So I'm not sure how offering pirates missions is supposed to work... but this experience didn't go to well.