I think BackRaiser didn't word it exactly right. It's not about empty hospitals. It was explained to me thus: The game will only check the first fifty hospitals in order of distance. So if none of those hospitals are valid targets (either full or filtered out by EMS Chief settings because tax is too high etc) then the EMS Chief will not transport. This was supposedly limited in this fashion to prevent excessive checks when there are tons of full or filtered hospitals nearby.
Yes, your 100% right