We are experiencing the exact same issue in our environment. Have you come up with a solution or a work around for this?
If the scanner is connected to the VDA, it works fine with MS windows fax and scan application. However, if you then open it up in the ScandAll Pro V1.8.1 it gives the error (SA01020E no scanner is found). The weird thing is if you disconnect the scanner from the VDA the software then is able to see the scanner, but then you get a different error (SA01081E You cannot use the selected scanner as it is not directly connected to the computer).