In theory it is illegal to file a false DMCA complaint. But the risk of facing any consequences from this is small.
I don't think you need to fear counter-suits since
most of the owners of the illegal sites are doing very shady things themselves, and spend lots of efforts trying to hide their true identity. I doubt that they would like to explain their business in front of a judge, also since they might have hidden away tax money in shelf companies on excotic islands.
If they did sue you, they would have to reveal their identity.
Of course you would need to make this assessment on a case by case basis.
Who are legit, and who are not. Most are not.
Since there is a good chance that you are dealing with criminals it is actually better for you to use bogus contact details to avoid blackmailing and threats of physical violence. Ultimately it could end up with face-to-face meetings with unknown persons, so you should prepared for such confrontations, if they should happen.
Probably filing fake DMCA notices is not a good idea for US-webmasters since US law apply for them. Luckily the world is bigger than that..
Good luck!
