A while back, Wolf of SEO, posted on Twitter asking are Google voice search results not impacted by the "non-mobile" friendly sites algorithm? He said he is seeing results that give non-mobile friendly sites.
So two things here:
(1) Voice search can be mobile or desktop based.
You can search using your voice on desktop:
You can search using your voice on mobile:
(2) The results you get are dependent on what you are searching on.
We all know that you can see non-mobile friendly results in Google's mobile results. So voice search has nothing to do with that.
Of course, Google Now, Siri and others tweak that a bit here and there. But voice search results are no different than the desktop or mobile search results interface. Unless you search natively on iOS or Android, then apps and such can show more often.
John Mueller of Google responded by saying that:
Forum discussion at Twitter.