My understanding from the documentation for PPI is that is analyses Perl Documents in isolation so I suspect there are simple cases where a regex may be provided by a module and used in the Perl Code being analysed that may not be recognised by PPI. However I don't have PPI available (it doesn't seem to be in ActiveState's ppm repositories) so I can't test that.
Note that PPI doesn't claim to parse Perl Code, 'only' Perl Documents. I agree PPI very likely suffices for the OP's purpose, but it's not clear that PPI invalidates the mantra. :)
DWIM is Perl's answer to Gödel