bhyve without UEFI questions

I'm getting conflicting information and thought I'd ask here about
guest disk images without UEFI.

1. If bhyve can boot the image with uefi-csm, should I be able to get
a graphical console? I tried:
   -s 6:0,fbuf,tcp=0.0.0.0:5900,vga=io
VNC connects, but the screen is blank. I saw some mentions of vga=on,
but that generates an error message.

2. Instead of using uefi-csm, can bhyve boot SeaBIOS? I've tried -l
bootrom,/tmp/seabios/out/bios.bin but I'm not sure that is working.

If one or both of these work, can you share the command line option? TIA!!

--chuck