This is really interesting, because I too always forget Apartheid SA had nukes. The question then is why didn't they use them? What forces or situations prevented that from happening?

Without going much into the history of said war, I think we can take Russia as a model for what to expect in regards of when can nukes be used, as russian nuclear doctrine is basically only use nukes if the state existence itself is threatened from outside. Nukes have always been a deterrent to prevent the existence of a given state from being threatened by another. During the fall of the USSR the nukes were not an option since the existential threat was from the inside. The question then is: was Apartheid SA existence as a state threatened by the defeat during the war or only its territorial conquest? The end of Apartheid came from both international and domestic pressures, no war to destroy the SA state needed, so the nukes were not an option. So, the russian model still stands: In Ukraine, the state is in an existential threat but they have no nukes and the russians have nothing to fear in regards of the position of the RF state, so no nukes needed.

When we get to West Asia is when things get complicated and dangerous. The question is: Is there an existential threat to the state of Israel? Could a regional war between Israel and the arab countries escalate to the point where the existence of the state of Israel is threatened? In the event of a regional war we won't be seeing a repeat of the 6-days war. The conditions have changed. The entire region may be dragged to the conflict and as many people have said in the arab-english speaking media: this may be the final battle against Israel. I've seen comparisons being made to Saladin or the Battle of Khaibar. Judging by this admittedly skewed vision, the arabs are seeing this conflict as existential to themselves and, even though no one really wants that, if they are forced to go to war they might be willing to go so far as to destroy Israel as a state once and for all. That is a war Israel cannot win, not with the current state of affairs, and that leads us to the nukes.

Since they officially deny they have nukes, we don't really know how many they can wield at any time. They can have just some tens of nuclear warheads, just enough to target strategic places without escalating further. Winning the war by nuclear means (or at least trying to, it may not even be a sure way to end it). Although the consequences of this would be another story. If they have nukes in the hundreds, they might be able to target places further out, like Pakistan, which could spark nuclear Armageddon, so it would all depend if they are willing to do so. This all boils down to if Israel has the need to use the deterrence card. I hope they don't, that cooler heads prevail and a war is avoided, but given the latest US movements (deploying troops and aircraft carrier battle groups to the Mediterranean), it seems the tensions are only going up.

So, to answer you questions:

Is there a way that Iran can aid Hamas without a risk of being nuked?

Clandestine ways I guess.

Is the only way to engage a nuclear-armed state guerilla war waged by internal dissidents?

Currently, most likely. Only internal pressures seem to me to be the most effective in this regard.

I honestly believe that regardless, we are looking at the opening salvos of the Third World War. I hope I'm (and I'm most likely are) wrong about all of this.