If that were something that concerned me, no, I would not accept that claim without proof. If you're making the claim, you should have evidence.
First, they aren't KNOWN to pose a serious health risk, they are BELIEVED to, and with good reason, but they are not KNOWN.
Next time there's a bake sale, ask the person selling the muffins if they know whether or not their muffins are diketone free. It may be perfectly logical to know if your product contains a whole constituent, such as walnuts as an example. Does this contain walnuts? Yes, no, could contain trace amounts... But for something that is somewhat ubiquitous in the flavoring industry, and can also be created as the result of a reaction between two other chemicals, I don't find it unreasonable that someone might not know.
However, if you don't know, don't claim to know.
but they are KNOWN to pose a serious health risk and from inhalation as the exposure... just because they are being inhaled by means of eliquid vapor all of the sudden that makes them safe now? I don't even think you believe that and yes the manufactures of eliquids have known this for a while now, years, and because no one was keeping tabs on them they could and did do and say what ever they wanted to instead of doing the right thing.