I have not been able to duplicate access via the ubuntu shim since I initially setup the configuration. It appears that the shim now checks the chained kernels or the secure boot code has been improved to check for signed kernels.
As for the raid-on issue. That is a known issue with the intel raid controller and linux.
I wish you well working with the 7400 2in1. I images ours last jul when they were first released. Those are interesting and finicky systems to image. Once they are imaged they are very nice computers. I can tell you the power button is only a suggestion to do things. Also if you want to get into the F12 boot menu watch the logo as it is powered up. As soon as the logo dims a bit then it will take the F12 key for a few seconds.