If you have proof that they are evading on another account, yes.

What if he is appealing, but his forums name is the same as one of his Alts. And he asked will that effect my ban? (Admitting he evaded)

He is allowed to have an account for appealing as long as he keeps the post there.

when staff don't use staff chat, 11/10

No, I'm talking about ingame. He evaded twice ingame after his main 2 were banned ;/.

Well if he was evading a 3rd time, ban him.

perm?

Do I ban just the 3rd alt, or all of them?

All of them.