For final settling of the bill, yes. For securing the reservation at check-in, not necessarily.

I have seen people pay with cash at chain hotels once in a while. But it's not necessarily their whole payment, and it's not likely their security deposit that's demanded when they check in.

Similarly, you may be able to do it for a rental car, but again only for final settling. You're not likely to be able to drive away with the car if all you present is cash for the reservation's stated rental cost. And for same reason, the rental company is not likely to accept the security deposit (even though they don't call it) with cash at pick-up time.