To clarify once again -
1) ImgTool is a separate program from Nero, not a built-in of Nero. It utilizes Nero's burn engine.
2) See #1.
3) So go to the place where you can check the program and test it for yourself.
Since ImgTool is using Nero to do its bidding, I don't see how it'll work if Nero doesn't...
Are you sure you didn't mistaken DVD+R media w/ the RW block below it and thought it's DVD+RW?