I'm not a lawyer, but I think there would be a defense. I believe states have to recognize other states legal acts if they have similar features and are not explicitly ruled out. That's what lets you move about the country i.e. out of state plates and license. So, say if a state other than California has stickers or maybe special plates you might have a defense. It's the kind of thing which really should be tested. With so many states having their own rules, putting onerous burdens on out of state travelers is one of the major reasons for our federal protections. I'm read somewhere here that Colorado was going to require a fee and a sticker to use public charge stations; that seems like a major burden for out of state travelers.
(I replied to the wrong article, the quote should have been one of the out of state issues.)
I don't think there is any federal protection regarding HOV access. Each state has their own right and privilege to grant special benefits to subsets of the population or merchandise subsidies as they feel appropriate to their state citizens. No reason that Texas needs to honor some of the stuff we do here in CA... and the opposite is definitely true also. (think concealed weapons)