In a fair world, each team would have been allowed to use the amnesty clause one time whenever they wanted to. Unfortunately, that isn't the case, the latest CBA stated that the amnesty could only be used on players currently under contract for the team looking to use the amnesty. So because the Celtics spent wisely during that time and didn't have any bad contracts, the amnesty essentially punished the Celtics.
In short, no, Wallace cannot be amnestied.