I tend to think that, for a lot of the time, there's precious little co-operation in the Co-operative. I see it more as a whole bunch of powerful interests balanced against each other in precarious equilibrium. The EF has its own principal purpose: to encourage capable, combat-trained pilots. From their point of view, piracy is a police problem, and none of the EF's business. The EF records might be protected, like client-lawyer discussions are supposed to be. Or like the Catholic confessional. If the police want to stamp out piracy, let them do their own work! Anyway, if law-abiding citizens were all well-armed and sufficiently skilled, then piracy wouldn't be an issue. What's required is not more police but more Academy places, and maybe cheaper hardheads and some subsidies on military lasers. Or so the argument might go.
Which is not to say that, in some circumstances, EF ratings information might not be leaked, or purloined, or somehow otherwise obtained, for legitimate reasons or otherwise. No doubt there are little power-struggles back and forth within and between the ranks of the police and the EF. But the EF's power would depend on its (supposedly) unbreachable seal of secrecy: it would be in its interests to protect this information. After all, information is power!
If you snatch a cheap kill here and there, where the cops can't see, you'll almost certainly be fine. But someone, somewhere, will have that information. That information will have a value. Commit too many secret acts of piracy, and maybe -- just maybe -- someone might decide that that information is worth cashing in. After all, those shiny gold Elite badges don't come cheap. And then there's the record keeping, security, overheads... perhaps a contribution to the EF fund is in order... thank you, most generous; you have a good day, now.
How many is "too many"? I'd imagine this kind of judgement is more art than science.
Edit: actually, there's an FE2 page on the wiki that covers some of this ground:
The Elite Federation has come under fire from human rights protesters in recent years due to their policy of not questioning what sort of kills are made. They will award kills to pirates and lawful pilots alike without issue. This has opened up many claims that they support piracy and terrorism. the EF answer these charges with the same defence every time: "...it is not our job to protect against lawlessness or to assign blame for actions beyond our control. Our job is to assign ratings. A pirate is still a pirate no matter what his Elite Rating - it is up to the police and the Navy to deal with their crimes."