If you dd the entire device, the drive label occupies one of the very first blocks to be copied. As soon as Unraid sees a second device with UNRAID as a label, it freaks out, for the reasons connervt very politely tried to tell you. I think you owe him an apology.
As an exercise to help you understand, please dd your Unraid stick to a file instead of a second stick, then open that file in a competent hex editor, as in one that works well with multi GB files, and search for the string UNRAID. You will find it very close to the beginning of the file.
BTW, if you insist on using dd to backup your device, that's fine, but you can't allow the resulting image to be mounted while Unraid is running, for the reasons discussed. Since Unraid attempts to mount any valid media, you must direct your backup to a destination that isn't immediately recognizable as a media device. Dumping to a file will work just fine.
Also, keep in mind that because a dd of the device includes the partition table and MBR, it will be inconvenient to use that image on a different boot stick as a recovery, because the new stick will most likely have a different geometry.
You could also send the output of the dd to a stick passed through to a VM, that way Unraid shouldn't even see it. You will need to work out how to pipe it across the internal network in the VM though.