I doubt he will be available. If he is amnestied, I would be shocked if a team under the cap doesn't make a bid for him, which would prevent him from becoming a free agent.
How many teams have cap space?
I am not positive with cap holds, etc., but somewhere around 10.
And, if I understand the rule correctly, a team could essentially win Roy for the vet minimum, if they were the only team under the cap bidding. And I am sure plenty of teams will put in at least a minimum bid, just in case no one else goes higher.
Teams over the cap don't even get a shot, unless no one under the cap wants him.