I don't have enough pipefish experience to go further with.
However for seahorses I have over a decade of experience that I can comment on to some degree.
Seahorse proofing includes covering any openings they may get caught in, including intakes, and making sure any output flow is not going to push them against something and damage them.
It means not having them with fish that can irritate them or outcompete them for food, even to just darting around the tank which can often stress a seahorse severely.
I'd never put any of my clowns, royal gramma, or tangs in with any of my seahorses, but then again, I only want seahorses in species specific tanks after earlier problems doing otherwise.
The tank should only have corals that are safe with seahorses as in no stinging tentacles of any kind. No anemone, and I don't recomment clams that can unexpectedly close on a tail that drags across the mantel.
While some have succeeded with other fish in a reef tank, even with non recommended fish, it's safer to go with the flow so to speak.
See the ratings at "
The Tankmates Guide".
I've never had an MP 40 but would likely recommend covering it with a mesh to prevent any tail injury.