Would an American citizen travelling from Japan to Israel on a tourist visa have an issue (legal or with airport security) if they don't have a return ticket?
The return ticket issue is more likely to be a problem at airline check-in. British Airways (but not a large number of other airlines I have used) hold strictly to the rule that you should have a return or onward ticket when you check in. They made me buy a (refundable) return. I doubt if the BA check-in clerk will be interested in judging if you are eligible for aliyah.
I suppose in the unlikely event that you are asked for a return ticket only on arrival (a question I have never been asked), you could short-circuit any problem by declaring an intention to immigrate.