In order for bluetooth communications to work, both devices need to have the appropriate "protocols" installed meaning that the types of communications possible have to be pre-arranged by the developer and hardware manufacturers. As far as I have seen, there is no such protocol established between the iPod nano and the iPad. This basically means that they aren't looking for each other and as such, won't see each other.
The benefit of Bluetooth is in wireless communication and exchange of data. Bluetooth headsets for communication and audio reproduction, Bluetooth speakers for audio playback, Bluetooth data connections for phone to iPad wireless tethering and data exchange. There isn't anything for the nano to do or offer to the iPad.
What are you hoping to accomplish?