no you dont NEED a mic when you have Ventrilo but its still fun to talk to everyone else on vent and if you need a link then look up left corner where it says Ventrilo Information click that and it says everything
lol if you dont have a mic prepare to get ragged on because you have no way to defend yourself! happens to Hardhat all day. He's from the tf2 side, and i hear the members get em everytime he comes in the channel. Pretty funny stuff. I hope if hardhat reads this, he realizes its all in good fun, and were waiting for the day he speaks up and blows us all away with a Berry White voice.
No, anyone can come in vent, and PLEASE DO, because its getting boring with the same old people.... but be prepared to see loads of em in private channels *coughCRIMSONcough* .