I found that by disabling the attempted use of the framebuffer I'm able to at least get oem-config to run. For anyone else hit by this problem, run the following before running oem-config-prepare:
$ echo "ubiquity debian-installer/framebuffer boolean false" | sudo debconf-set-selections
This will update debconf with the setting necessary to instruct oem-config not to attempt to create a framebuffer.
I found that by disabling the attempted use of the framebuffer I'm able to at least get oem-config to run. For anyone else hit by this problem, run the following before running oem-config-prepare:
$ echo "ubiquity debian- installer/ framebuffer boolean false" | sudo debconf- set-selections
This will update debconf with the setting necessary to instruct oem-config not to attempt to create a framebuffer.