It wont matter if its just a few. I was meaning that when they hatched you may have a problem. When I had frogs I decided to try hatching some dragonflies, except then one morning I wake up to around 10 buzzing in the tank and the frogs didn't even eat them Then when I went to get them out they escaped! My cockatiel got a real fright >.>
Same thing goes for mozzies they can be a real pain because they're harder to see. In general if you keep a lid on it you should be fine, mozzies cant get in and lay the eggs and hatchings cant get out, everyone wins, and hopefully you don't wake up with bites all over you!
Another thing is to make sure is that you don't get the giant dragonfly larvae. Ive seen ones with a 15cm wingspan! beautiful insects :]
Anyway, I'm no expert so don't take me too seriously