It looks like, per https://github.com/librerpi/lk-overlay#what-features-work , yes you can boot to Linux on a Pi 2 with composite video and ... it doesn't use the word headless anywhere, but I'd be very surprised if you can't just omit video outputs completely.
EDIT: Actually, reading more carefully it looks like there might be more than one blob and it's not 100% clear to me which this replaces, so now I'm less sure that you can boot without any proprietary blobs. I'm not sure that you can't, but I can't tell.
EDIT: Actually, reading more carefully it looks like there might be more than one blob and it's not 100% clear to me which this replaces, so now I'm less sure that you can boot without any proprietary blobs. I'm not sure that you can't, but I can't tell.