Hi Peter,
The raw disk image has been used to deploy 1000's of devices world wide. It is specifically designed to make it possible to deploy on any whitebox bare metal appliances that don't have a VGA or CDROM available. If there is a better way I would be happy to test it.
As per the post, it seems there are errors during writing to disk. This is a bad sign, since I suspect problems with the hardware later could be possible. Personally I would be hesitant to go into production with a disk that experiences write errors since the byte cache is extremely disk intensive and given enough time, will break a drive already on its way out. Possibly it could also potentially be read errors from the USB that are shown as write errors during the copy.
Other potential issues, that I don't think are relevant but to provide a full answer:
Booting with the USB and physical disk connected with the exact same raw disk image is not recommended. They are two clones of the same drive and problems do occur. After writing to disk, disconnect the USB. Or better and recommended, flash the physical drive with the raw disk image from scratch.
It could be that some RAID and SCSI drives are not compatible with the generic linux drivers. In the case of RAID it sometimes works to disable RAID. Certain SCSI issues can be resolved by running the boot image from another drive and mounting the datastore on the SCSI drivers for better IO.
Another alternative when driver issues are suspected is to use the Ubuntu image instead of the Core Linux image.
If for whatever reason all else fails, VMware ESXi can be loaded on the hardware and Wanos loaded as a VM.
Lastly, all the hassles of installing the software can be avoided with the Wanos appliances.