I don't have any scientific proof one way or another, but my bees love borage and I eat the honey and I'm still alive. I have never heard of borage nectar being toxic in honey. Maybe if you had 100% borage honey? I know deer don't like borage so there must be something in the plant that is a bit toxic, but I don't know if that transfers into honey in any significant quantities. There are many other toxic (to mamals) plants that bees forage all the time, so I would not worry about borage specifically. Again it is my personal, non expert, opinion.