score:1
So the answer to this is apparently yes, Scanned copies of invitation letters and filled out sponsorship forms , invoices ,bills etc are valid.
What did I include:
I can state this because I just received my visa that had the scanned copies of above attached for all but my own documents.
However, I cannot guarantee it will be valid for all countries , cases or categories. This answer relates only to my case in which the only difference between the earlier rejected application and the successful application were sponsor's documents as scanned copies, which I believe were the sole factor for the application to be successful this time.