Any crab or shrimp is very vulnerable to predation when they molt. And it's not just fish that will kill a shrimp or crab, they'll likely do each other in if the opportunity arises. Cleaner shrimp are an excellent example, they're monogamous and a dominate pair will kill off others if there's a group of them. Individual personalities will vary and how well fed is a factor but I've had melanurus with shrimp for years without issue.
I have two of them, 1 large adult and one small. Also had one for about 3 years that I lost. Never had them touch any of my shrimps. I have a few different varieties of shrimps in my system but as you know with fish you always have the risk of a rogue fish. E.g. My sailfin started biting chunks out my trachys and acanthos.