So you chainload SeaBIOS, and try to boot the bsd.rd and it don't show
nothing? Your conclusion
is that it's because don't have framebuffer?
I don't know exactly how is the boot process on OpenBSD (although I
use it daily), but I don't
think that it require framebuffer to boot.
What do you are using to boot? A plain snapshot of install57.iso
burned on some CD-ROM?
You tried the pxeboot?
If nothing works, you could try compile with aperture driver disabled:
http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man4/xf86.4?query=xf86
And, reduce the secure level:
http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man7/securelevel.7?query=securelevel&sec=7
If not working, try the openbsd-misc and request some help (please,
send some dmegs and dmidecode/biosdecode logs).
Regards,
--mutus