You don't need Region mode to find the RDP window. You'll use Win32 mode and you can identify the RDP window based on its window title or the process name.
One or both of the following worked for me when I've done this:
Window Title: ""*Remote Desktop*""
Process Name: ""mstsc""
After you launch/attach to the RDP window, you then use region mode inside of the RDP window to look for images and text. You'll obviously have all of the same concerns as any time that you use Surface Automation, such as the screen resolution of the machine, font smoothing should be turned off, etc.
Dave Morris, 3Ci at Southern Company