I haven't heard of or experienced Dragonets being aggressive toward tankmates, but there are always exceptions.
Although I own a Sailfin Dragonet, I have been very successful training him to accept Mysis from my hand. Additionally, many others on RC have had great luck with getting their Green or Psych. Mandarins to accept prepared food.
Of course, I still recommend a healthy in-tank pod population, but it's nice being able to sleep at night being certain that Scooter is eating well regardless.
The trick is getting food to fall into his general area so he can "discover" it. Initially it was happenstance, but if you want to target feed, you have to be a little more deliberate. I did this by wiggling the cube above and behind his field of vision, letting pieces drift into his immediate territory. Over time, I moved my hand further into his field of vision, to the point where he now swims toward my hand when it's feeding time. The trick is to be slow and deliberate with your movements, or they will become spooked and speed away, until they are totally comfortable with your presence.
These guys and their eccentric antics are a barrel of laughs, especially when they're well-fed.
(The Dragonet equivalent of the TANG POLICE) 8)