The main blobs are being run on the GPU, as bootloaders, even before the actual operating system is loaded. OpenBSD does not need to run _any_ blob itself.
There used to be a 3d graphics driver blob, but afaik that got open sourced. Also, if you don't do 3d, you wouldn't even need it.
I don't know exactly what the situation is. Don't care. I have a BeagleboneBlack if I wanted to watch the paint dry doing a build. :)
The rPi boot process requires several files to be on a FAT partition on an sd-card: bootcode.bin, fixup.dat, start.elf, config.txt and the OS kernel; the first 3 of which are blobs.
Would those blobs need to be included, or would OpenBSD be fine saying "use your existing boot card, just drop in our kernel", or "go grab these files from https://github.com/raspberrypi/firmware/tree/master/boot when formatting the sd-card."?