Asking if it's ok seems completely appropriate, particularly if you're in someone else's home or car.
Even though there may be a reduced health risk, most vape products have an odor that other people may not appreciate, and that smell may linger.
It may just be my perspective, but when making changes to a shared atmosphere it's appropriate to ask. Even with more innocuous things like adjusting the temperature, or turning on a radio, if you're with others and you're not sure, ask.
As a side note...
I've known a number of smokers who switched to vaping because it was less regulated. They could vape indoors in places where they couldn't smoke and so on.
Once upon a time smoking was common enough that people wouldn't think twice about lighting up in most places. As people became aware of the health issues, the etiquette adjusted and people were expected to ask or excuse themselves and go outside. My point is that the customs changed over time.
Vaping being a realitively new thing, the etiquette is still developing... But in a lot of places it seems to be being treated more and more like smoking.