If the account is on a different server

it wouldn't matter, yes? lol
Some players attempt a way around this by doing, something like you're suggesting, a separate account in control of the guild/bank; with farmer toons depositing into the GuldBank.
It really depends on the GM doing the investigation during the initial ban of the first account.
If a second account is online when a first is being investigated they may ban anything that is indirectly related to the first if they can prove connection.
They don't always follow transactions, no. I've mass-purchased keys through single and multiple paypal accounts/card transactions (prepaid) with mixed results.
What I have noticed is if I get one account snagged and others are online, regardless if they are on a separate IP/box 8/10 times they will also be banned/locked; if they aren't online at the time of the investigation, rarely does something occur.