You can change the prompt it is expecting by adding <Command Name="VirtualPrompt" Value="$"/>
However I too am unable to backup these devices. Every thing works except I get no output from the "config -g config" command (or from "cat /etc/config/config.xml" command) Works great when I logon manually to the device, just not in solarwinds. it is as if enter was not pressed. SCP does not work either as I cannot enter the password. TFTP may work but I am currently having an issue with the TFTP server.
I got it to work - In addition to the above DON'T set
allocatePTY to false. use this:
<Command Name="AllocatePty" Value="true" />