After a while if the union succeeds and becomes strong enough it will get its own nukes. If North Korea can do it, a union that is several times larger, more populous and wealthy can do it. Yes it will scare the shit out of many countries, but at some point our economy and influence would be too important to the world economy for us to care what they think.

For Israel to use nukes successfully they'd have to do a preemptive strike (which won't be easy to justify to the international community) and be damn sure they nuked everything that is a threat to them. This already assumes a lot of things like the fact they'd be sure it won't lead to them getting fucked by the international community or start a world war which will likely fuck them up, that we wouldn't have a defense system against nuclear warheads, that we wouldn't have allies that would destroy them etc... If they don't do a preemptive strike they are likely screwed, because it's a tiny country and you don't really need nukes to do crippling damage in a short amount of time. If they send nukes the forces already inside or too close to their territory will only find even more reason to raze it from the map and fight to their last breaths.