I should add that as a circumvention, a BSD disklabel can be manually added. The FAT MBR partition starts at sector 243 for a size of 4018957 sectors. Manually add this using disklabel(8) and its -E option or -e option. Here's a quick guess at admin inputs using disklabel -E, to create an "i" BSD partition to align with the MBR partition, just as an example:
Code:
$ sudo disklabel -E sd1
a
i
243
4018957
MSDOS
q
y
I have not actually tested this, these responses to questions from the disklabel -E editing tool are from memory. I have no OpenBSD platform available to me at this instant. If you do this, read the prompts from the disklabel program and answer appropriately.