Any blenny as long as it’s reef safe should not be actually hurting the corals if perched on them. Same as others like Hawkfish. Sure they may distrub the coral and sometimes irritate. Another example is a Tang. Sometimes unwanted algae grows on and/or around the coral. And the Tang will peck at it trying to get the algae. Sometimes it will end up nipping at a certain coral part just enough to get the harder to reach algae spot, but that is nipping, not eating or destroying it. Should the Blenny whilst trying to get the algae on/near the Zoas ends up damaging the coral, something yiu can do is move the coral to a higher flow area. Algae shouldn’t grow on coral unless it’s in low flow or the algae is taking hold of a weak coral IME.