Yep I would never trust them alone together either. We have my mom's dog which is Captain and is a Rot/Pit mix who thinks he is a teacup size dog LOL, he is a sweet heart and funny enough I might trust him more than our 2 goofs but nope not getting near my nibbler. Then our 2 we have Trixie who is a Chihuhua/Jack russell mix and Bear who is a Pompoo. Bear is about the only one that I do not think could hurt Nibbler only because he can't even bite his own dog treats well LOL And once Nibbler is an adult will be bigger than little Bear bear LOL. Bear is also the first one Nibbler tears off after, Nibbler LOVES hair!! Lol
Its just best to keep them separate though.
We also have a cat and she could care less about Nibbler. She took one look at the duck and ran off like nope nope nope not even going near that.