"Bardic Music: Rat-a-tat levels stack with bard levels for the purpose of determining the rat-a-tat's daily uses of his bardic music abilities (if any) and the value of the bonus granted by this music."
Well, there is the bit though about them not ever being able to leave the city.Also, any permanent-duration ability that carries no expense can get very powerful, very quickly. Every day that your rat-a-tat has nothing better to do with his music, he's going to animate another item. It won't take too long before he's got every bit of trash in the city serving him. To balance this, you might set some limit on the maximum amount of such items he can have at a time... Perhaps 4 times his class level in hit dice?
So, I mean, if the campaign never leaves the city, and he uses up almost all his bardic music in one go for days straight it 'is' possible... so I dunno.