Okay, i can't say this for sure, but since your not getting any replies i'll throw in my 0.2 cents...
Depending on the type of eel your planning on putting in with them, i'd be worried about the dwarf puffers nipping the eel to no end since they are known to be nippy and aggressive... but in all honesty, most people will tell you its a gamble mixing a puffer with any fish... so unless you don't mind losing an eel / puffer, i'd probably not risk mixing the two species...