I'm not sure if this was tackled or addressed from previous posts.

Can Tyranids include Neutral cards for deckbuilding? Thanks in advance!

We won't know for sure until we see the rules insert for The Great Devourer expansion.

That said, the deck building rules from the LTP guide in the Core Set imply that neutral cards can be used in a Tyranid deck. (The Tyranids lie outside of the alignment wheel, but the deck building permission to use neutral cards is a separate rule from the alignment rules.)