When customer buys new domain to be mapped...what DNS servers?

Domain mapping: Hi I have a simple question as I'm new to DM: If a customer buys a domain only to be mapped to my site and not to go with any other hosting, can he leave the DNS servers blank? In namecheap they suggest setting up DNS servers but in this case the customer wouldn't have any. Unless, should he put in my dedicated IP? Then he'd still have to go set up an A Record? thanks.