I would not consider this salable any more, even if you clean it and test it, unless you provide full disclosure as to what happened.
I have in the past successfully cleaned a keyboard that had OJ spilled in it, and dried in it. I soaked the keyboard in water for a minute or less, rinsed, and blow-dried. (Those were tough times for me financially, or I would have just bought a new $10 keyboard).
However, a keyboard has little to no chance of damaging the computer it is connected to. I'm not so confident about a PCIe card. Personally I would toss it because I'd be worried about a short or something causing damage to the Mac Pro. The value of a used 5770 that has been peed upon is too low.