The point is that the regulations to a good part predate the state of Israel. Only marriages of same religion people are accepted, except for some cases. Accepted in this sense means recognized if the people (more or less) are living in Israel / are Israeli. You can also say that you are not religious and marry non religiously and it will be recognized.

The things are messy, but not as messy as some people make it out. They are a consequence of in the early phases of the state letting marriage handled by the religious institutions themselves. Then the social conditions, their respective positions and the aims of the factions influenced each other leading to the current situation in which there is a part tradition, a part bourgeois politics, a part election politics and materialist power politics.

So in the case of the tweet, yes they could marry. They just have to say they aren't religious or convert. Compared to the laws that repress our LGBTQ comrades in terms of marriage, child upbringing, adoption it seems to hit more people, but to be easier gamed.

The recognition of ethical poly is also something typically not found in states' marriage laws.