Many ECE standards are higher than DOT/Snell. If the rider can show that the helmet met higher standards, even if not technically DOT certified I think they would be ok in the long run.
Ok with who?
See the fundamental issue is when would this statute actually come in to play?
As has been mentioned, a peace officer (apparently) can not cite for DOT compliance.
Can an insurance company deny claims because you were "violating the law"?
But if you are not cited, then how do they know you were violating the law?
An ECE standard may be higher than DOT/Snell, but it is also, notably NOT DOT compliant -- thus against the statute. It can't be sold in this country, and it's illegal to wear in this state IN ORDER TO COMPLY WITH THE LAW.
Which brings up another question, are helmets required for off road use? If I'm riding a pit bike at the track without a helmet, is that against the law?
If not, then if I'm wearing an ECE helmet on my pit bike and fall, since I've not "violating the law", an insurance company wouldn't be able to use the fact that I'm wearing a non-DOT helmet as a reason to deny claims (unless there's a clause in the policy regarding helmet use, of course, they anything goes).
So, like a bunch of other laws, when is this one going to reach actual contact with a citizen. I don't see this happening in a courtroom, unless for some silly reason a DA is piling on the charges.
"Not only was this person riding at high speed in a school zone, when they struck the crossing guard in the crosswalk, with an illegal exhaust system, and illegals bike lighting, they were wearing an illegal helmet!!"
"Charges: Manslaughter. Riding with out proper lights. Riding without a DOT helmet. Riding with a loud exhaust. Failed to yield to crossing guard."
And then there's simply whether insurance companies are able to deny claims due to illegal activity.
So, in the end, just not sure when this really matters any more.