He was in company C with the 1st Florida Cavalry, Union and of the men whose records indicate they served at Marianna, there aren't any company C men. The three companies who appear to have participated are A, E and F. Isaac is listed as doing duty as a nurse in the regimental hospital in October 1864 so he likely didn't participate.
The northwest Florida and southeast and central Alabama area did become increasingly anti-Confederacy as the war dragged on. I'm not sure from all my research that it was pro-Union as much as anti-Confederacy. At the beginning there were more Cooperationists than pro-Union men. They wanted the south to secede in concert not individually. Many of these folks then decided to wait and see. The Confederacy rapidly started stepping on the same "states-rights" toes that the Union had stepped on. With the Confederacy it was the draft, taking the brigades from the state's control, impressment, etc. And then at some point when things got really bad here, folks just started cooperating with the Union who had always had a presence here. Survival instincts will trump almost everything else.
I am sure it was quite ugly around here for a few years after the war. People were tired, angry, hurt, resentful, and hungry. All emotions that tend to lead some to look for scapegoats. Some believe the Union kept the 1st Florida Cavalry in serve until November 1865 for that reason. Concern for their welfare. There is a high percentage that disappear after the war. I plan to discuss that in some detail in the book I'm working on.