Verified. Stage 1 and Stage 2 (at the very least) Brown Bears give Orc Warriors. Neither one shows this. The building display (when you click on it and open up the info) shows only Vallorian Guards, and when you collect from the building, you only see the little Vallorian Guard heads floating upward. The evolution preview (you can open this on the "Evolve" tab) also does not show any additional production for these stages. But you do receive the Orc Warriors anyway.
One sample city:
- Brown Bear Chapter V Stage 2
- Vallorian Guard units per squad: 54
- Vallorian Guards obtained per collection from bear: 22
- Orc Warrior units per squad: 161
- Orc Warriors obtained per collection from bear: 84
Update: They give Orc Strategists too! I almost didn't notice, since I do have two Grounds of the Orc Strategist buildings, but as I write this, I have not collected from them today. (They are still sitting there with their collections pending.) When I took the before/after screen shots, I had 81.8 squads of Orc Strategists before, and 82.3 after. I didn't even think to look at the flyovers to view the specific numbers of units overall, but there are 161 in a squad, so probably I received 84 of those as well. (I'll try to record it next time.)
I am not seeing any signs that they give any other units though. Notably, they do not give Frogs.