A debat has begun about wether or not it would be necessary to complete an OFAC verification on existing customer prior to estanblishing another new account even if you verify your institutions entire customer database each night?

It would seem to be overkill.
If you scrubbed your database last night and the next day an existing customer opens another account, it is highly unlikely that they would be on the OFAC list.

It would seem to be a very low risk transaction, however you should follow your OFAC Policy and Procedures.

Remember that you are doing the OFAC on the Customer, not the account. If you have already done the OFAC scan, and your system scans all customers each night, to catch the OFAC updates, then an additional OFAC check when opening a new account would not be necessary.

If your procedures/policy states that an OFAC check must be done on each new account opened, then you will need to get those changed.

(I also saw your ACAMS listserve message, but it is easier to answer here)