Someone hiring you and not paying you is a breach of contract but that's not the same as piracy. If I download the latest Hollywood blockbuster for free, I've not breached a contract because I didn't enter into one (though I may have breached a contract with my ISP). The offense committed is copyright infringement and in many jurisdictions this is a civil offense rather than a criminal one (or, as in the US, there are conditions to turn it into a criminal one that very few downloaders would satisfy).
Not if the contract is itself illegal and/or immoral. A contract is not necessarily enforceable by virtue of it being a contract. But this is a straw man; the point is that the terms "piracy" and "theft" have been misappropriated to protect intellectual property, bringing along a lot of basic assumptions that can be justifiably challenged. Even the term "intellectual property" is vulnerable for the same reasons. The whole debate takes place in a virtual world where not everyone agrees to the same conditions. But the same could be said about the ownership of physical things, which probably originally meant whatever you possessed at the moment (a piece of food, a scrap of clothing, a hand weapon) and was eventually extended to mean whatever you could protect over longer periods of time (livestock, shelter, huge tracts of land). The concept of ownership is continuously evolving.