> Has Israel even officially confirmed they have nukes?

No. There's a number of reasons for this. #1 is Israel's policy of "strategic ambiguity" and #2 is that it might be illegal to even mention it in Israel. Israel prosecuted a whistleblower nuclear scientist for leaking state secrets, for example.

> And who have they blackmailed with the nukes?

The US, for one:

"Similarly, in the 1973 Yom Kippur War, IDF was again outnumbered by the invading Arab armies. Then Israeli PM Golda Meir authorized a nuclear alert and ordered that nuclear warheads be readied for launch from missiles and aircraft. The Israeli ambassador to the US, Simcha Dinitz, met with Henry Kissinger to inform President Nixon of “Very serious conclusions” if the US did not airlift arms supplies to the IDF. Nixon complied with this demand due to the threat of the use of nuclear forces. This was the first successful use of the Samson option as a threat and tantamount to nuclear blackmail."

from: https://thesvi.org/deconstructing-israels-samson-option/

I also recommend: https://www.currentaffairs.org/news/wait-why-is-israel-allow...

The Samson Option enables Israel to blackmail the entire Middle East, and do so silently. Turkey or Egypt can't afford for Hezbollah to overrun Israel, because Ankara and Cairo might get nuked, even if they had nothing to do with contributing to Israel's existential crisis. It basically forces the whole neighborhood to keep each other in check out of sheer self-preservation. Credit given where credit due, it's a smart approach on Israel's part.