I don't know what goes on in a commercial setting, but it seems like people just need to be careful. If they aren't they need to go since care is essential in this line of work. With decent people, I wouldn't feel unsafe with a basal tie. Rigging would concern me more since it may not always be easy to see the exact path of the line. Couldn't you untie the bottom, bring the rope up, canopy anchor for the work, then drt exit the tree?