In limited fashion, yes, for the secret door. Unlike in (Umineko Spoilers) the revised rules of knox for umineko the rules for a hidden door under knox specify no more than one, and only if it is foreshadowed heavily. However, there is no such exception for things such as local diseases, poisons, etc. and that is because while the presence of one can be inferred from clues, its easy enough to make it work very much in a way that isn’t easily predictable.
Its a bit of a fundamental difference as to -why- the things are banned. While it would be hard to infer the existence of a secret passage, and it allows for rather lazy writing as well, the specifics of a secret passage are rather easily understood and universal. They allow passage from one area to another. The specifics of hard to understand scientific devices and unknown poisons and diseases, on the other hand, are not, and sort of act as a bit of a non-magical magic so to speak.
At least, this is what I have found in my own exploration of the genre. As I said, its not really a problem in higurashi though since it was not designed to follow the same conventions as a golden age detective mystery, so it isn’t exactly bound to them. It works very well as a modern mystery, its just not solvable in the classic fair play sense.