They can- they do not grow aggressive when terastallized due to how the Tera Orb harnesses and causes the phenomenon to manifest in tamed pokémon. They grow just as strong in what their Tera Type is as a wild pokémon does in theirs.

[There was just the Type Advantage that needed to be thought of when going into a Tera battle, of course.]

I don't doubt it, especially from what I have seen here- or simply heard of.

[Clavell didn't actively seek to fight in this world, but he would head into one if he was there rather than turn and run after all.

Houndoom lifted his head up when he caught the movement of Eevee, moving closer just in case they did get loose- Houndoom was one of the man's pokémon very used to young starters after all, and honestly enjoyed being there.]