I think many CPs will admit to knowing and talking to other companies CPs. I have heard first hand from various CPs that they have asked others for info and references. I don't know if it would extend to salaries and conditions for all its pilots. I do know that some airlines have "agreements" with others not to poach their pilots. I have a friend who applied to BA and BMI and got a job with BMI. Shortly afterwards BA called to offer him a job. He happened to mention in passing that he'd already got an offer with BMI and the BA option was withdrawn. Have heard this sort of thing before. I remember Geoff Hall of Monarch saying that if he knew a pilot was breaking a contract with another airline he wouldn't employ him.
Also, I have been on the receiving end of the "old boys network". Again, proof was the problem. Twice he got me, but ultimately I think I got the better deal, a good job with a good airline, and his word was rubbished as I proved that what he had said was total nonsense.
I knew exactly who the person was and who he had spoken to but nothing in writing. I even had contacts in the company and they looked through the files to find out if there was any reference in writing, but no.
Be wary, aviation is a very small industry.
Even if you don't annoy someone, if they take offence to you, even if its for no particular reason, you could find yourself getting seriously hindered in your search for a job.