The LLC’s ownership and Montana registration are not inherently tax evasion.

The appropriate party can pay California or New York use tax arising from the vehicle’s in-state use. Whether Montana registration may legally remain or California requires a registration from you for a vehicle you do not own is a separate question. Generally, the LLC registers it. Since this vehicle has had its use tax already paid, the tax evasion argument won't apply.

Now is vehicle registration evasion a real thing or something you made up to conflate your fear mongering with legality?