And this is a bad thing because...?
Forgive me, but I personally cannot fathom why it should matter to you whether they hatch the eggs or not. After all, you're getting paid either way, so I fail to see the detriment if they decided they wanted to try hatching the eggs. Once the transaction is...
Cat purr sounds are probably an indication of contentment, much like with an actual cat. My chickens make the same sound sometimes, and they are all perfectly healthy.
Recently signed a pledge to refuse cage eggs, in order to help free future battery hens from the daily horrors of their existence via the following link:
http://www.animalsaustralia.org/no-way-to-treat-a-lady#pledge
None of my current personal experience even remotely suggests that any degree of tameness has a detrimental effect on a chicken, male or female. Quite the opposite in fact, the more a rooster or hen identifies with you on a personal level, especially as chicks, the less aggressive they seem to...
I suppose a pair might be necessary, if your intent was for more than protection...If their role is strictly protecting the chickens, then their mating practices would not be relevant.
As to the Hawk question, as far as as I know a hawk is perfectly capable of carrying off a full size chicken...