Getting Pirated by a freelancer

[The Savage]

So, to make it clear for sake of wording:

Combat - when pirate initiates combat, freelancer does not join.
Defence - when pirate is fired upon, freelancer is defending.

Otherwise, Pirate ID cannot hire Freelancer ID at all, according to what you wrote. Drrobe's rule clearly states that Freelancer ID cannot be hired to help to attack trader if the latter refuses to pay. It says nothing about Freelancer defending Pirate.