I think 'consider them to be whichever is better to you, as the ranger' is reasonably clear, but I'm happy to clarify.

>Hypothetical scenario: Let's say your character has gnome
>hatred. Presumedly, if you're fighting a gnome shapeshifter
>who is OUT of form, your edge will be in effect.

Correct.

>However, if that gnome shapeshifter shifts into, let's say, a
>reptile or rodent form or anything but a gnome, will your
>GNOME hatred edge still be in effect?

Yes.

And if they shifted into a tiger, you could apply feline hatred if you had it, or gnome hatred if you had it. If you somehow had both (only possible if the second is a reward), you could apply both.