I am not sure how the entire process works at your bank - but would a teller that had this level of authority possibly be able to book advances on the system without anyone else being involved? Or would they be able to possibly book loans which were fictitious? Since it is a teller then there would be more options available to misappropriate the proceeds of the loan due to them having a cash drawer available, however, this does not mean that it cannot be done.
If there are steps in your processes that would mitigate any risk of misappropriation of assets then there very well may not be any problems here. In my bank we have a number of tellers who also book notes on the system. In fact, we have a number of loan operations employees who are also tellers. It all depends on what other checks and reviews you have within your system.