I played with it a bit and as soon as one adds "ou=..." or "dc=..." to the binddn it raises an error. In this example config and in the "real world".

Imho there aren't any limitations to the binddn option?

No, there are no limitations on binddn. Your example is invalid since you have not loaded any schema to define the "ou" or "dc" attributes. The error message from slapadd is correct.