Interesting idea - is it multi-accounting to start a new account on your old server - don't see how.

If you have had an account closed it is technically no longer yours - otherwise you'd be able to access it. Therefore you have no account on that server and if you start a new account or are given one it cannot be called multi-accounting, because you can only access one account.

As Dawnseeker has so agressively stated that evonys' policy is that no closed accounts will be reopened, you cannot be expected to assume you will get your old account back even if you are innocent. Therefor you have no account on the old server.

If your banned though that is different, because you have only lost temporary access. So starting a new character would be multi-accounting.

I haven't seen any mention of a person being banned from the server, so if you stick with one account you in theory should be alright.