I know two CD keys cant be used on the same sever. But if me and a friend played brood war on different servers at the same time quite often, could I expect blizzard to do anything, like ban the CD key?

Don't think so. My (old) key is usually in use in every single gateway simultaneously all the time for years, and Blizzard didn't do swat.

O ok thanks. Why do you need accounts up on all servers?

CD-key usage for logins is only checked per gateway afaIk.
But I don't know if Blizzard checks for the same key being active at the same time on different gateways, but I personally doubt it. But it's your key and you decide.

You could still play on the ICCUP server.

Not rly me, just, uh, around 20 people using same key at once

EDIT: And thus we can also conclude Blizzard doesn't care about how many different accounts logging into the same key one after another either

You can install spawn copies, but they can only join games hosted by the original.

Does spawn even work on battle.net?

Oh yeah, it does, you can hang out in chat channels and stuffs, too.