You may see some SWR variations as you rotate the hex beam. My original mounting location had it mast mounted from the ground but partially overhanging the roof. In other words, about 1/3 of the antenna was over the roof and 2/3 was in the clear. As the driven element was rotated over the roof the SWR would rise beyond 2:1 on some bands. I don't know if it didn't like being close to the roof or if it was caused by the fact that only part of the antenna was over the roof.
I haven't read about similar effects when the antenna is mounted on the peak of the roof. Of course that is not an option for you.
Will it work. Absolutely. Is it worth the effort. Absolutely.
If you paint, go for a flat paint. Less reflections. I've painted various items with Krylon Camouflage paint. They call it ultra-flat. It's carried at my local Home Depot but not Lowes.http://www.krylon.com/products/camouflage_paint_with_fusion_technology/