It depends on the personality and age of the dwarf freshwater puffers. I had guppies, platties, otos, and one dwarf puffer for over 3 years together, and never had a death or nipped fin. Tank was heavily planted and the puffer was the last thing added. Kept well fed, they CAN do ok but it really depends on the puffer. A lot say only a species tank and had I known that when I purchased the puffer, I would not have bought him. He was the exception I think, rather than the rule.
They love snails. I had gotten him to get rid of an overpopulation of snails (now I know that they overbred cuz I overfed the fish...duh....). Once the snails were gone (less than 3 or 4 days in a 29gallon tank), I fed him live California black worms and frozen bloodworms. They are not fast eaters, and I had to feed him with an eyedropper to prevent the rest of his tankmates from taking the food intended for him. I'd wait until he was near it but the rest were elsewhere to release a worm. He quickly learned to come to get his 'bottle' as my husband laughingly called it, at feeding time. He'd chase (briefly, and not nip fins) the rest away from 'his' food once he learned that it was for him alone.
Here is a link with a lot of good info about them. Most say its ok to mix them with the Oto. If it is the dwarf freshwater puffer, it does indeed mean FRESHWATER, not brackish or saltwater.
Dwarf Puffers : Home
Hope this helps. For your 10gallon tank, I'd only do one or two puffers. They need 5 gallons or so per fish and depending on the gender, you may get some fighting if they are overcrowded.