When it comes to fish eating livestock I personally consider anemones to be grouped with corals. I don't know why, I just figure if they'll munch on an acan, why not a nem too. Sure them nem has a defence mechanism, but some fish are too stubborn to give up that easily!
I would only trust a puffer with nems if it came from another one if my own tanks, or a trustworthy friends tank who has kept that particular individual before with no coral/nem eating issues.
Just my 0.02 :)