I wonder how capable Iran is in supporting Yemen. If you look at the map you will see that no common border exists between those two. Furthermore we know that the American Navy rules the shores around the gulf and Arabia. America is far from neutral in this conflict and have at times taken some military action along Yemen shores. So how do the Iranian weapon get there? There would be only precious few which could be smuggled in under hose circumstances. 
Now in Lebanon the geographic and political situation is totally different. The Shia population ie. Hezbollah is 40% of the population. Through Syria and also Iraq, Iran has plenty of physical access to Lebanon and Russia could also provide a weapons pipeline via Iran to the area. So if the Saudis have problem in Yemen it would certainly be much worse for them in Lebanon. In fact the only chance they have is if Israel joins forces with them. The ruling elite of the Saudis might see no problem with that the common Arab certainly will.