The only way for an object to enter Tel’aran’rhiod would be for it to be carried there by someone who entered physically rather than through a dream state. If left there, it would remain until it was retrieved by someone else who entered physically. And, yes, an Aes Sedai could free herself of the Three Oaths with an Oath Rod created in Tel’aran’rhiod, but remember that relatively few sisters actually have access to the World of Dreams, and for those who do want to remove the Three Oaths — sisters joining the Black Ajah — there is the Oath Rod in the White Tower to serve that purpose.