Yes. Well, let me put it this way: you can do what you like, but if you want a shot at mutual cooperation it's got to be really easy for other bots to verify that you're willing to cooperate. The more code you put between them and 'C, the harder it is for them to verify your niceness.

A stronger version of this statement is "put as little code as possible between them and discovering that you cooperate". This implies that your predicate should be similarly simple. If you want my advice as to strategy, your predicate should be along the lines of (equal? ((eval them) (degredaded-quine me)) 'C).

That seems a little arbitrary.

It's quite arbitrary. The "real" rule is that your 'C can be as deeply hidden as you like so long as you don't scare any bots into defection when there was a chance at mutual cooperation. My bet is that there will be a bunch of twitchy bots, and my suggestion is that you put your intentions front and center.

Your mileage may vary.