Yes, if the jurors were actually paid off, the verdict could be vacated.
FYI, I just looked into the situation you mentioned.
The jury foreman bought the property in 2008 as tenants in common with the "lawyer on the deed" you mentioned, who was probably his girlfriend. She is a young lawyer and doesn't do criminal law BTW (and there are about 94,000 lawyers in Florida, so we certainly can't assume they all know each other).
The Complaint that began the foreclosure proceedings was filed April 25, 2011. The jury foreman and his girlfriend sold the house on April 27, 2011. Presumably the mortgage was paid off as part of that sale, because it was released by the bank for full payment on May 16, 2011.
ALL of these dates were before the jury was selected in Casey's case (May 21). Moreover, the sale of the property provides an obvious and totally innocent explanation for the payment of the mortgage.
ETA: The May 26/27 date people are throwing around online is the date that the bank finally got around to recording the release of its "lis pendens." It had already signed the mortgage release (May 16), recorded the mortgage release (May 23), and filed the release of lis pendens in court (May 24).