The floating plants probably help limit algal growth by taking up nutrients. I have not run across any info that indicates floating plants, in any way, increase algal growth!
Byron can speak more eloquently on the topic, but I believe floating plants help a good bit with algae control, as long as they don't shade things too much. My limit for floating plants is about 25% of the surface and I "corral" my floating plants using suction cups and black thread barriers to keep them where I want them on the surface. I keep my floating plants over my lower-light plants, or over specific parts of the tank where algae starts to reappear once in a while.
I currently run my lights at 7-7.5 hours/day, even dosing with Flourish Excel daily. Six hours of light didn't seem to bother any of my plants when I cut if back for a two-week anti-algae effort. The only plants it seemed top bother were the ones I was already having issues with, the Cabomba and Myrophillium that like pretty high light.
It's absolutely a light length/intensity issue. It can be exacerbated by nutrient excesses, but as Byron said, light is the key element be it intensity or duration of the light.
FYI - My hair algae never "died back", it just stopped growing and I had to eventually either removed it with a toothbrush or removed the infested plant part with the attached algae.