I can create now recipients by a workflow and see them in the the start page under "Profile and Targets".
But I can't see them under my self created folder of recipients in the explorer view...
How can I solve this ?
Inside the workflow that creates recipients, there should be an Update Data activity where you are perforning inserts.
You will have to add a new element i.e. Folder and specify the folder with which you wish to tag these recipients.
Every Recipient has a link with schema xtk:Folder. If you don't fill the correct value for this link, all recipients are created with folderid as 0 and hence you cannot view them in Explorer view.
Hope this helps.