In the summer of 2010, the Heat waived James Jones to free up cap space due to the unguaranteed portion of his contract, then signed him a few weeks later to the veteran's minimum. So there is precedent for waiving a player to save money then re-signing him.
If a team waives a player, it allows other players to claim that contract and it loses Bird rights. If the player passes through waivers, the team can sign him using available cap space or a salary cap exception.
I think the NBA would probably step in to prevent re-signing a player who negotiated a change in the guarantee as part of the buy-out, since this would be a way to work around the rule against renegotiating a change in salary.
Now that I say that, I think that may have been what happened with Keyon Dooling. Negotiating a buy-out then re-signing him to the minimum would be the same as renegotiating his contract to a lower amount. So, the league may have stepped in and said it wasn't allowed.