When financial institutions/market makers are trading regulated derivatives they will have USD on deposit in their accounts to speculate/make a market/trade. In the event they were to not close a position, made an error, etc,they would be obligated to purchase or deliver the actual XRP. To do so they would need a way to accomplish that as they are not necessarily holding crypto on their books in a wallet.
These institutions are not usually dealing in small amounts and would need somewhere to fulfill their contract obligation such as a gateway setup to Ripple.
Probably why he used the phrase lender of last resort, but I'm not gonna speak for him.
Liquidity is not always the way that most retail investors think of it. If a financial institution has to buy $25,000,000 worth of XRP they are gonna have a tough time getting that done on a crypto exchange without running up the price versus going direct to XRP who will give them one price.
When these contracts are listed on a regulated US derivative exchange you are trading the derivative, not the actual XRP, however if you get stuck on a position for whatever reason you are gonna have to come up with the actual XRP. That's where Ripple may come in to play.