My questions is:

If an Accountant borrows money from a company and does not put the amount on the books or the balance sheet, what kind of account should the loan be recorded as later on?

If the person is borrowing money from the company he/she works for then the company would record the transaction as follows:

Debit Accounts Receivable - (Name of Person who borrowed the money) for the amount
Credit Cash for the amount

If the person is borrowing money from another company on behalf of his company, then the transaction is posted as follows:

Debit Cash for the Amount
Credit Accounts Payable - (The company that lended the money) for the amount.

If the person borrowed money from another company and it is a personal loan then his/her company would not record the transaction.