in reply to Hire a Perl programmer and get a database guru free?
Over half of them are quite well-versed in database work and have built both the data and code for at least one reasonably sized application from scratch. About a third of them are triple threats: They could build a reasonably sized application from scratch including all of the required systems design and administration.
It sounds like the person you're looking for may be someone who can do just that: Take a set of requirements and do everything except perhaps the system administration. They may be working in somewhat of a vaccuum if there are no other DBAs on staff.
In this case, I would highly recommend focusing not just on whether a candidate has built data-centric applications using a database similar to the one you would propose to use, but on whether they have designed a data solution (e.g., everything from the table structure including constraints to indexes to triggers and stored procedures if necessary). Ask them to sketch an ERD for a schema they've designed on a whiteboard during the interview to make sure their skills live up to their claims.
Being able to pull information out of a database is a whole different beast from designing a schema which is reasonably efficient, scalable, and extensible.
I also second Ryszard's comment. With some projects you are best off hiring a bright but inexperienced (and inexpensive) coder. However, when you hiring someone to be a one-person band, you get what you pay for. If you are looking for someone to single-handedly take the project from requirements gathering to initial release or beyond, you will save yourself time, money, and heartache by paying more for someone with more experience.
Hope this helps :-)