Interesting, had to look that one up and it appears to be a Canadian thing. Other Toyota hybrid vehicle owners in Canada are being told the same thing. Most don't trust the Toyota\Lexus 10 year treatment no surprise there. The official reply from Toyota\Lexus Canada seems to be this canned response:
With hybrid models, application of aftermarket rustproofing such as an undercoating product, could affect the high voltage leads. As such, the application of the product could camouflage the orange high voltage leads resulting in emergency, dealership or independent facilities personnel being electrocuted or shocked if they unknowingly touch the high voltage lead.
It is always the customers decision to add or not add this type of product, however, with the company adding the product would have to be extra careful so as not to hide the high voltage leads.
Overall the canned response seems a bit vague on warranty. Laws are different in Canada then the US. That was hammered home when I was hunting the Sunset Country of Ontario last year and a CO walked to the back of the truck and opened the lid to the topper. My first thought was hey you can't do that without a search warrant! Wait in Canada he can. He was a young First Nations guy and came back to me and asked me how old my Nova Scotia Duck Tolling Retriever was. Then pulled out his phone and started showing me pictures of his Toller, all smiles and all good. Spent the next half hour talking dogs, bird hunting and Tollers instead of him trying to find if I broke any game laws.
In the US the Magnuson-Moss Warranty Act allows aftermarket parts and things like undercoating but it isn't applicable in Canada. So not sure what the correct answer is there. If it was me in Canada I'd probably go ahead with the Corrosion Free treatment, but that is me. Not sure if there is a Canadian National law or Provincial law for Ontario may be worth looking into.
Corrosion Free is what the Canadian military uses to protect their vehicles. It is similar to FF and the first year had my Taco I tested Corrosion Free 3000 against FF on steel wool plus a control piece of wool. Sprayed the wool with a mixture of water and road salt once a week and kept them in my heated garage. Why I park outside, heat is a catalyst for rust. 20 to 30° below zero Fahrenheit not so much.
Control after 4 weeks
CF3000
Fluid Film
Corrosion Free is some good stuff, it is oil based and better than FF. But after the first year it jumped in price and have to get it from Canada so I switched to FF. For 11 years climbed under the Taco in the Fall and did it myself. Still got some rust but better than without it I'm sure.
On my GX I had NH Oil Undercoating done professionally it is basically FF on steroids DuPont beefed it up with a lot more creep and adhesion. After watching him apply it in places I never dreamed of doing with a high pressure wand I will never do it myself again. I was cleaning it up for months afterwards as it creeped out of body cavities including going UP on the outside body panels. In a couple of weeks I'll have woolwax done, professionally on the frame as it has more wash off resistance.