Yes, they will. If they could, they would make you pay twice! Check old forums for the past few years, it is their pattern. They will probably offer a "sucker deal" just in time for you to buy it, but not be eligible for the update. I have fallen victim of that twice.
I was worrying about this but so far my parallels installation has worked without a hitch in Yosemite.. Didnt even have to update it, it just didn't break.. Which is very unusual for Parallels running on a DP!
The guy from Parallels says that Parallels 9 will support Yosemite in an update. They support 2 years of versions backwards ... if that makes sense. If they come out with a Parallels 10, they will support Parallels 9 and 10 with Yosemite.