I wouldnt chance it. The butterfly would probably be ok but the puffer is going to always go after the shrimp. you might get lucky if you get some bigger shrimp but i still think the puffer would be all over any shrimp big or small.
My puffer loves cleaner shrimp.......for dinner! You can put a whole bunch in there and you should have shrimp for a little while, until the puffer can catch them all. Those shrimp can move!