Sure it is. It would hardly be the first time a guy being traded in his contract year was talked to pre-trade to determine interest in signing an extension or even having one hashed out before hand (with permission from the trading team of course).
In fact, I'd argue that those conversations in this type of scenario happen more often then not.
If Shattenkirk tells a team outright he has no interest in signing and wants to test free agency then you might be able to get him with a guy like Spooner and other significant pieces.