I have an old Screaming Eagle harness that uses a very similar rope as Amsteel. It's bury is "secured" (stitched, if you will) with zip-ties.
I've used zip ties for a lock stitch for ground level use when I was experimenting with bridge length. Never experienced anything unsafe about using zip ties, but it was a short-term deal. I assume long-term use would be okay, but we all need to assess our own risk thresholds.