I don't know the official policy, but anecdotally, I won with an entry that used libperl back in 2000: http://www.ioccc.org/years.html#2000_dlowe

I love this bit of history from the hint :)

Aside: history... Larry Wall wrote the original Perl in 1986-87, the same two successive years he won the IOCCC. I hope this program helps you to realize that this was no fluke - that Perl and Obfuscation are as inseparable as, say, camels and humps.

The fact that it won for "worst abuse of the rules" doesn't help your point much. :-)

Generally we don't like lots of external dependencies. External libraries do change over time - would such an entry work 10 years from now? The judges do use and test the entries using different operating systems. What will operating systems look like in 10 years?

Having said that :-), if the entry has merit on its own and not just because of the external dependency, then it might "win".