There is nothing wrong with outsorcing DNS - for example I use EasyDns.com.
But an increase in hits - only a moron would think that was true. The way DNS works is, it gets cached in a billion places all over the Internet, so if you browse to
www.xxx.com, you don't even go to the DNS server since in all liklihood somewhere upstream from youits already cached somewhere.
And even if its not cached, *your* pc will cache it on the first hit so whether it will take 20 ms or 50 ms is hardly important. You won't be hitting that nameserver again for probably 24 hours.
The salesman is an idiot.