It doesn't matter how skilled the programmer is when you're only seeing the surface level. The website is simply your interface with whatever the developer chose to implement. A developer's website is meant for communication, and if it serves that purpose, then it has met the sole goal of a developer's personal site.
A canned implementation with a default theme, doesn't mean the developer hasn't tweaked something on the back end to make it easier for him deliver content. Nor does it mean the person wouldn't make your ideal employee.
Web development on a personal site level doesn't indicate anything about knowledge, skill, or abilities, especially since any real developer will be using a server side language for the bulk of their logic. Development for a personal site is still just barely above scripting, and any technical person can do that with any number of the frameworks and languages in use today.
Whether the person rolled their own, or used someone else's doesn't indicate one way or another that they are capable of solving real problems or have any real knowledge of development work. Therefore, as everyone else has indicated, their content is much more valuable in the evaluation then the platform on which it is communicated.
The same goes with designers, check out their work and portfolio, not the platform or theme of their site.