Apparently the pirates who captured the Maersk Alabama were involved in negotiations on board a US warship when their hostage was rescued.
Normally I would be concerned by this - it is important to keep faith, even with people who don't deserve it, so as to maintain a reputation in future.
But here, I can't see a problem. The principled position would be to refuse to negotiate with pirates at all. That is difficult in practice, because of the human element, but if this means that it will be harder for pirates to negotiate in future, that just discourages piracy - negotiating the ransom is an essential part of the process for them.
If pirates know that the authorities will negotiate with them (even though they really shouldn't), but will double-cross them at the first opportunity, that is more of a problem for the pirates than for the authorities.