Hi Jellyweb,
Yes it is possible. All you need to do is export your joomla user from your database into CSV format and then upload the CSV file in your backend > easyblog > subscriptions > import subscribers. However I just tested the importer and it seems like there are some minor bug that causing the importer not working correctly. Before you begin with the import process, kindly download my attachment below and place it inside your /administrator/components/com_easyblog/models/ folder and see how it goes.