Yes, you can write real perl 6 code, using a subset of perl 6 because perl 6 isn't finished yet, and therefore doesn't really exist. You can also write real perl 6 code using perl 5, because at least some perl 5 code will run unchanged in perl 6.

Mind you, I didn't know that Rakudo had got that far, so thanks for pointing it out.

update: building rakudo fails because 1GB of memory apparently isn't enough.