It's pretty much that. If there's a dog humanoid monster in a sexual scene, the tag should be added, even if is one single small scene. Why? Because some people get offended if you don't tag it properly. They even will say stuffs like "you lied to me" and such.
Dog humanoid monster should fall under the "monster" tag, not the "bestiality" tag, they're f'n different things... Someone looking for one of these may not be looking for the other.
I'm also of the firm opinion that tags should be added based on presence and relevance, not based on the desires of special snowflakes.
Like the tentacle tag... The amount of tentacle content in this game is pitiful. If was looking for games based on that tag, and ran into this one, I'd be thoroughly disappointed. Even when it comes to tags I dislike, like scat, I won't avoid a game with it if it has ONE avoidable scene or some such. I've seen it happen after all... It makes tag filtering meaningless, because you might filter a perfectly good game that might have just one bit of content that you can easily avoid.
Ugh. I swear. This comes up all the time, and people keep being brainless about it...