<<If someone says No, period - doesn't that mean they will vote No regardless of what happens between now and the meeting? >>
I wouldn't assume that without them saying it, you can if you want. It is your survey.
<<so his vote (or non-vote) ends up being a yes vote in either case>>
No, not unless something has changed from what I have been used to with other companies on votes like this. If a vote is not made, I don't believe it counts, for or against.
Maybe most don't really care about the survey, so we might be wasting our time.