Checking dotable.com @ archive.org for July 2006, when I signed up, shows _all_ accounts came with custom nameservers. Bob was then using his "DOT-1", "DOT-2", etc. scheme for accounts. It was about six months later that Bob changed from the DOT-scheme to a more standard account setup with "multi-domain" accounts, "reseller" accounts, etc.
http://web.archive.org/web/200607210...w.dotable.com/
(Both of my Multi-Domain accounts have custom nameservers)