What if they just want to do treatments, consulting, add planting. Do they still need to know the knots?
I think that's good for anybody wanting to do overhead work. A pretty base level of competency.
Since you bring it up, I don't know that I have taught the few people I've helped start climbing more than 4-5 knots... Figure 8 (do you count on a bite as a separate knot?), clove hitch, a friction hitch or two, I guess an overhand and slip knot technically count. That's about all I ever use on the job. Learned a whole bunch in Boy Scouts back in the day, but trying to think through what else I use on the job...