JerryDan Strangely, turning down the notification vibration slider down to the second lowest option significantly reduced the strength of the unlock vibration haptics. Turning it down all the way makes it full strength and obnoxious again. This is an AOSP issue, not a Graphene one (there's a thread on reddit about this from Sept).
There's no way to disable this vibration entirely while keeping the rest of your phone vibrations (in other words, you have to disable vibration and haptics entirely if reducing the notification vibration strength slider isn't enough). It seems that Google either didn't test this at all or doesn't care about people who prefer to have the unlock haptics disabled. I'm leaning towards a bit of both, seeing as the "fix" to reduce it involves affecting notification vibration strength, which is very strange.