I worked for an oil rig company in a different state from where I live. While employed, I got into some trouble and was convicted of a felony and put on probation. I later failed a drug test for my employer and was fired. Can my employer give my probation officer the exact reason that I was fired?

Of course. Your PO is part of law enforcement. Aren't you obligated to tell your PO yourself?

Yes and you should expect them to, in fact are you not suppose to report being fired ? And what will you say when they ask you why ?