Generaly, I can answer this simply: I'd certianly take up a position like this in my current job, if the job required it. I'm Director of IT and head gopher -- by defintion, if the job requires it, I do it.
I wouldn't be comfortable doing it, though, and I /am/ a web programmer, by initial learning of perl. Really, I'm a generalist -- I could probably pick up the basics of DBI/SQL fairly quickly, but I would probably do it poorly for quite a while.
Is it reasonable to expect to get a Perl programmer who can hold their own with the DB? Certianly, if you ask for it: "Perl programmer firmilar with DBI/MySQL wanted for (part|full) time employment in the (long|short) term. Around $N, depending on experince". Make sure you interview around their rel. experince in the various fields -- you're end up getting a number of people who are good on the DB end, but barely speak perl, and vice-versa. (BTW, if you want DBA-ish stuff -- designing a DB, admining it -- say so, if you mean "can query against an existing DB using SQL", say "SQL".)
Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).