It absolutely could work. There are drivers in all the float parades, they could be adapted to work similarly. If not it is also common to have stagehands, puppeteers etc in full black that are very visible in shows but the black allows them to fade from your focus. This would be especially true with these floats because they are so bright and vibrant your eyes will be on the animals etc not on the guy sitting low driving. AND they are not close to the seating and out there in the dark.
JBA drivers were barely visible and I don't think I would have even noticed them had I not been focused on watching all the technical aspects. This show is not human-less, there are entertainers out there already, a guy with a low presence in black would not be a problem. Many great performances and forms of art use guys in black. Even can be done creatively like the puppeteers in Nemo. Costuming makes them part of the set.
This seems more about stubbornness on Disney's part to want to claim a technology in their show or not pay for modification and extra people. WELL given what it has cost them to run this thing to now almost the beginning of the eighth month late, their money could have been better spent. AND given the difficulty they have had with the man-less floats there is probably a good chance this will be an ongoing issue.