It is not snake oil. When TreeSpyder called my attention to the lightning hazard I remembered many hours I spent on the internet researching, and the advice of an electrical engineer, concerning lightning protection for my boats. I am assured the same basic principles apply to trees. From what I found and heard there are two methods of protection that both make very good engineering sense.
1. Dissipate electrical energy before it reaches high enough voltage to make the jump (lightning). Electrical potential dissipates from sharply pointed conductors (the "Lightning Rod" approach).
2. Provide a "Safe Path" with a well grounded conductor big enough to carry a significant portion of the charge safely to ground. Few "Safe Path" conductors small enough to handle in a tree or boat are big enough to carry the whole charge, but besides "Sidetracking" the majority of the charge they might also localize the damage from the remaining charge. Besides, much lightning damage is caused not from the main bolt, but from "Side Strikes".
I witnessed the effectiveness of "Safe Path" many times offshore. Our rig and production platform flares were routinely struck (and lit) by lightning with no damage to our platforms. The strike went straight to ground through the metal platform legs. I never saw even a little single-jacket (one well) platform no bigger than my bathroom damaged by lighning strike in 25+ years offshore.
It is a statistical game. Your client should know you cannot guarentee 100% protection. But the best information I can find assures me you can lower the odds significantly.
I'm sure it is not worth worrying about in Oregon. But in South Louisiana or Florida - worry. Maybe you cannot sell "Lighning Protection" service, but you can certainly offer "Lightning Hazard Mitigation" services in clear conscience. Rodding and cabling a tree doesn't guarentee a crotch won't fail, but it significantly lowers the odds.