Is there any way to retrieve all blobs uploaded by opponent?
There is no basic way to retrieve all blobs of the opponent as all files are kind of private.
As a workaround you can use Custom Objects API http://quickblox.com/developers/Custom_Objects.
For instance, create UserFiles or UserAlbum table and put all files (blob IDs) you would like to open to users in it. After this users will be able to get all data from this table using user_id= filter.