Israel is a sovereign nation, the Houthis are not.
Under international law, the attacks of a nation are the responsibility of the attacking nation. The same is not true for independent militant groups. For example:
France arms Ukraine and Ukraine attacks Russia, Ukraine is responsible. Iran arms Houthis and Houthis attack Israel, Iran is responsible.
So then in that case, Hamas attacking US embassies is completely fair game for arming Israel?
Israel is a sovereign nation, the Houthis are not.
Under international law, the attacks of a nation are the responsibility of the attacking nation. The same is not true for independent militant groups. For example:
France arms Ukraine and Ukraine attacks Russia, Ukraine is responsible. Iran arms Houthis and Houthis attack Israel, Iran is responsible.