This took forever. The AI is a pain.
Tested this with my Armorouge against
a Hippowdon. After about 40 turns of being read completely by the ai, it eventually went for Rock Slide, which was blocked by my Wide Guard. The animation triggered over my allies as well and I didn't see any of their health drop thay turn so it going with Yes, Wide Guard works in Tera Raid Battles.
Update did get to test this in a raid with friends and they confirmed that Wide Guard Blocked Moves for them.
Hope I Helped.