This feels like a dumb question, but I haven't been able to find an answer. Loan customer pays the closing costs of a loan with cash over 10,000. The loan officer brings the cash to the teller line for deposit. The customer does not come with her. Do we list the loan officer as a transactor?

The loan officer is accepting the payment on behalf of the bank just like the teller would had the customer walked up to the teller line. The loan customer is the transactor for the CTR.

...and it was the loan officer's job to obtain all the information required to properly complete the CTR. Suggest that next time, he walk his customer to the teller window and let the customer deal with someone who knows what they are doing.

I remember a loan customer coming in to payoff a truck loan with cash in a brown paper bag. I didn't even touch the bag. I walked him straight to the tellers. I hope your lender counted the money in front of the customer and had the customer agree to the amount. You don't want the customer saying later I gave you $10,200, and the teller counts only $10,100. Lenders should be made to understand that they are not tellers.