Multiple sites say that's not the case - from USnews.com:
Securities Lending Programs
Online brokers, such as E-Trade, Interactive Brokers, Fidelity and Charles Schwab, offer this option. The fees are typically split equally with the broker.
The brokerages lend out the securities to third parties such as traders who want to sell short, says Andrew Wilkinson, chief market analyst at Interactive Brokers. Individual retirement accounts, or IRAs, are also eligible to participate in the stock lending program.
"We split the fee received from lending stock 50-50 with the client," he says.
From Investopedia.com - if you have a margin account you get zippy from loaning out shares:
Benefits From Loaning Shares
When a trader wishes to take a short position, he or she borrows the shares from a broker without knowing where the shares come from or to whom they belong to. The borrowed shares may be coming out of another trader's margin account, out of the shares being held in the broker's inventory, or even from another brokerage firm. It is important to note that once the transaction has been placed, the broker is the party doing the lending and not the individual investor. So, any benefit received (along with any risk) belongs to the broker.
The broker does receive an amount of interest for lending out the shares and is also paid a commission for providing this service. In the event that the short seller is unable (due to a bankruptcy, for example) to return the shares they borrowed, the broker is responsible for returning the borrowed shares. While this is not a huge risk to the broker due to margin requirements, the risk of loss is still there, and this is why the broker receives the interest on the loan.
The main reason why the brokerage, and not the individual holding the shares, receives the benefits of loaning shares in a short sale transaction can be found in the terms of the margin account agreement. When a client opens a margin account, there is usually a clause in the contract that states that the broker is authorized to lend—either to itself or to others—any securities held by the client. By signing this agreement, the client forgoes any future benefit of having their shares lent out to other parties.
Interactive Brokers says it's a 50-50 split even if the shares are in a margin account:
https://www.interactivebrokers.com/en/index.php?f=46942
Program Overview
Earn extra income on the fully-paid shares of stock held in your account by allowing IBKR to borrow shares from you in exchange for cash collateral, and then lend the shares to traders who want to sell them short and are willing to pay interest to borrow them.
Each day that your stock is on loan, you will be paid interest on the cash collateral posted to your account for the loan based on market rates.
IBKR pays you 50% of the income it earns from lending the shares.
The program is available to eligible IBKR clients1 who have been approved for a margin account, or who have a cash account with equity greater than USD 50,000.