1) The US is considering plans to invade or bomb Iran if negotiations fail.
2) If that were to occur the second worse thing that could occur (the first being Iranian use of a nuclear device) would be if the Iranians could successfully prevent oil tankers from going through the Straits of Hormuz. The removal of 13 million barrels of day from the world markets would be quite a shock to the world economies.
As can be seen from this graphic, UAE along with part of Oman is on one side of the Straits if Hormuz. Iran is on the other.
My guess is that we would benefit by having access to fields on UAE and likely Oman as well to support our ships trying to keep the strait safe for oil tankers in the event of conflict, perhaps for additional landing fields for planes and/or for antimissile batteries.
Though I don't think a deal was ever present (port control for bases) if the port deal doesn't go through the UAE government may be unwilling to allow the US to make use of UAE soil in the event of conflict with Iran. Certainly UAE would be making itself a potential target. Perhaps the potential for refusal has been privately communicated to the Bush administration by the UAE government