The major powers and the arabs knew Israel had or was in the process of developing nukes long before anybody heard the name Mordachai Vanunu, there is no point to having nukes if the enemy doesn't know you have them otherwise they are not a deterrent to war. Ambiguity was an American idea, Israel did not sign the NPT and chose to develop nukes which was all perfectly legal under international law but there was pressure on the US to pressure Israel to give up its weapons, but it actually suited the US to have a nuclear ally in a region dominated by Soviet client states so they came up with the idea of ambiguity where you neither deny or admit and so it allowed the US to turn a blind eye. Its an arrangement that suited the US and Israel because the mental fear of the unknown can be an even more powerful weapon than the weapon itself. It, also suits the arabs. Olmert nearly blurted out on the record Israel had nukes and he was then given a warning by the Saudis that if Israel had nukes then they may feel a need to develop their own nuclear weapons program. Ambiguity is a game played for the sake of diplomacy and its worked just fine for the past 40 years so why change the policy now? IF IT AINT BROKE DONT FIX IT.
Iran deal opposition grows among U.S. Republicans, Reuters poll shows (Reuters)
from the article: Israel's nuclear ambiguity no longer serves a purpose