I say it's not necessary.

I started in Perl without access to any *nix computers. Come to think of it, I don't think I've ever programmed significantly on Unix (apart from sql scripts), though I certainly wouldn't avoid it.

Am I a Perl Master? No, though I'd like to think I'm somewhere above novice. Most of my work has involved accessing databases, manipulating files, with a bit of ASP perlscript, pulling emails from my accounts and processing them, etc.

I certainly don't think I won't have a chance to fully learn Perl because of a lack of Unix. Actually, I suspect learning Perl will help me somewhat if and when I do need to use Unix. It would serve as something familiar, at any rate.

Of course, part of this could be the effect of not knowing what I'm missing. Perl's served my needs quite admirably. :) As for whether you'll be able to find a JOB knowing Perl but not Unix, that's a separate question.