I don't think it has anything to do with a broker whether or not they lend out your stock... but rather it has to do with your account.
If you have a margin account then you can bet your A$$ they are lending out your stock... especially if they are getting 20, 30, 40% on it... but if it's a CASH account then they CAN NOT lend your shares out without your permission.
IRAs... Roth or SEP can only be a cash accounts... personal accounts can be either or.
You can turn a margin account to a cash account anytime you want to... but of course if you do, all stocks must be fully paid for.
But after all is said and done... I don't believe they honor those rules... if they have a stock that they can lend out in any account I believe they will.
Hell... some brokers even lend out stock they don't have - you know - Naked Shorting... and I think most, if not all do it.