That's not too surprising, pretty cool actually! They'll help keep it all clean
I actually think shrimp are safest with either the biggest or teensiest fish. Maybe a P would go for big big shrimp? If I may ask, could you post a video of you feeding the fish?
You are absolutely right , I think that an Amano or Bamboo shrimp could be eaten but Cherry shrimps are just to small. My Cherry shrimps don't hide at all and often swim just before my manny's mouth but the manny pays no attention to it. I will try to make such a video but a problem is that my manny eats when the lights are off
You can see Red Cherry Shrimps on the pic below (there are hundreds of them):
One more pic :
All my Vallisneria plants died because of lack of phosphate, I've just ordered some Cryptocoryne aponogetifolia and nutrition capsules which contain nitrogen, phosphor, iron and micro nutrients.