Does the word dokter have two correct plurals? I could have sworn that another sentence used dokteren.
It does, and both are accepted:
Could you leave out "zijn" and this still be correct?
Similar to how you can say "Ik directeur"?
No you need a verb, Ik directeur is also not correct Ik ben directeur.
Maybe you are trying to refer to the fact that you can leave een out.
The audio doesn't say this.
Here it does.
I keep hearing something like "Jullie is een doktress" am I totally crazy?
But for sure I hear an "i" sound after Jullie :s
Obviously I don't know exactly what you are hearing (though it should be the same), but on my phone and laptop the pronunciation is correct.
Ok thank you
Does this both mean hospital doctor and doctor as in graduate?
Dokter = medical doctor
Doctor = academic doctor
(link in Dutch) https://nl.wikipedia.org/wiki/Doctor#Doctor_versus_'dokter'