An interesting question. A single kobold could probably sneak in and keep a low profile. However, trying to walk the streets or draw attention to itself is something else. Assuming it lived to escape the town, it wouldn't likely come back. The tavern is, after all, in the center of a human town.
They look like small lizardmen, and would likely be set upon fairly swiftly. As a result, I'd class them like animals; a quick in for a bit of excitement, then out, but not as a continuous character.
I will listen to arguments to the contrary of course, but for the moment, they can't stay in the tavern for any length of time.
Siani, who may have to revisit the monster rulings soon.