Did he tell Dani that she was safe after winning HOH or are you talking about their conversation during Thursday's show? I still think it would be dumb to nominate the 2 floaters because Dani could win veto and remove one, say Kalia. You are then left with Jeff having to nominate one of Adam, Shelley or Rachel. There are 5 voters and Dani + Kalia control two votes, needing only to convince one to keep Porsche. Dani's alliance could enter the Fast Forward intact. And even if Porsche leaves, the replacement nominee is now against Jeff.
The net result is that Dani retains two loyal followers, while Jordeff are stuck with 2 of Shelley, Adam and Rachel. As you said, a very shaky alliance.
Cut Dani and the other side doesn't have any glu to stick together. Jeff solidifies his alliance while he weakens the opponents.