The original vision for Perl6 included a runtime called Parrot which would have been capable of running both Perl6 and Perl5.
If Parrot had been realised, Perl6(Raku) and Perl5 would have been able to interop similar to how Java and the other JVM languages can.
But without that, Raku and Perl remain incompatible so e.g. the existing large Perl ecosystem can't be leveraged from Raku.
Au contraire, they remain compatible along the lines shown in this example from a StackOverflow answer[1]:
use Text::BibTeX::BibFormat:from<Perl5>;
...
@blocks = $entry.format;
To be clear, the realization of Larry's original vision is not constrained to interop with Perl. Raku has extraordinary potential, some already realized, for pan-language compatibility via its Inlines[2].
The steady improvement of the exemplar Inline[3] for the last 6 years; its evident maturing; its suitability as a solid blueprint for upgrading all the others; all of this bodes well for being able to use a lot of the world's best existing code from within Raku this decade, with Inline::Python quite plausibly shining in this regard within the next 2-3 years.
[1] https://stackoverflow.com/a/45181464/1077672