With due all respect, I honestly don't see any meaningful help from Iran. May be some missile and drone knowledge transfer took place, but with the absence of anti-ship and air defense means, the few ballistic missile and drones that got intercepted won't mean much.
Setting up an effective air defense network against modern fighter jets is a highly complex endeavor. It took Iran itself years to reach that point. The AD network has to be integrated, multi-layered and has to consist of enough units to cover a large area. Support from fixed and mobile, bulky radars as well as EW and communication devices is required. Overall, SAM weaponry is technologically more sophisticated than ballistic missiles or UAV's, therefore it is also more difficult to successfully smuggle into Yemen the numerous parts which make up a SAM system, because contrary to many of the BM or drone components, they can't be produced locally, and thus every interception of a shipment by the enemy will jeopardize a whole effort. Then there's the need to adequately train teams manning the air defense systems. Politically, due to the international arms embargo a degree of plausible deniability is required, which in the case of Yemen is given with drone and missile technology but not with SAM's.
Do the math - it is too high an expectation for Iran to be able to single-handedly supply Yemen with a useful, survivable and cost-effective AD network in the midst of the war and considering geographic constraints. Under these circumstances, the best option for Yemen are compact, loitering aerial ambush munitions, in other words the now famous unnamed Iranian missile. And these Iran did ship in numbers towards Yemen, as proven by intercepted cargoes of which pictures were shown to the public.
As concerns anti-ship missiles, Yemeni forces did fire several of these during the course of the war, hitting an Emirati military vessel and reportedly even targeting an American one, and it is entirely plausible that these missiles were supplied by Iran. Just as the unmanned suicide craft (or related technology) which was successfully employed to strike a Saudi warship. This said, I'm not sure how much of an effect it would have on the military situation if the Yemenis made more intensive use of ASCM's, considering that anti-ship missiles just like drones and ballistic missiles can be intercepted and more importantly, that it's not its naval arm the enemy is using to strike Yemen. Targeting international shipping across the Red Sea represents a theoretical escalatory option, but for obvious reasons ought to be considered a last resort and is definitely not as justifiable as missile and drone attacks on Saudi and UAE (military) infrastructure.
So to sum up, given how Yemen is completely surrounded by adversaries, given how it is placed under UN arms embargo as well as naval blockade with the participation of the USN, and given the distance that separates it from Iran, the wide range of ballistic missiles, cruise missiles and UAV's Iran managed to either transfer to Yemen or help Yemenis assemble and field domestically, has been the militarily rational choice, the most effective means of retaliation logically conceivable, and in and by itself a rare feat few states would have been able to pull.
I would also not under-estimate the considerable impact Yemen's BM's, CM's and UAV's have had on the military balance. Without these weapons, it stands to debate as to whether Yemen would have been able to resist this long. I understand the frustration at the constant stream of images of Yemeni civilians perishing under the bombs of the aggressors, but you have to observe the situation in a sober manner and take into account every relevant circumstance. Honestly, when doing so it appears that the assistance Iran has achieved to extend to Yemen in the face of serious adversity and complicating factors has been pretty much impressive. Don't forget wars aren't fought to score higher kill ratios than the enemy but to achieve pre-defined political goals. Given the UAE's structural dependence on foreigners (workers and investors alike), it is fraught with an inherent vulnerability to any sustained threat that could potentially scare away these foreigners, which is why these Yemen's drones and ballistic missiles are of immense significance even if intercepted.
