| Hello, alexh. You could try but understand the challenge first. Here are some differences between these two types of plants: Hibiscus, as you noted, will become deciduous and start looking ugly sometime in the Fall. You can prune the stuff above ground though and then see if they return for you in Spring. I grow the hardy ones in my area (they are perennials here) and I begin to prune the stems when the leaves begin to fall down and the stems turn light green or yellowish. But if that temporary look does not get a nod of approval from you, try something else the following year. Camellias have a lot of shallow leaves so try not to dig or do disruptive work around the canopy of the camellias. You also want to leave some separation between any all plants to make sure that you do not get any form of fungal infections in the leaves. Keep an eye on the size at maturity that is specified on most plant labels.
Sunlight is a big problem. Camellia leaves will want protection from the warm afternoon sun during the summer while Hibiscus just absorbs all the sunlight that it can take. If you cannot strike a good sunlight balance between these two different plants then you better not plant them together. Base your shaded and sunny observations of the fence on what happens during the summer and not on how things look like now.
I let camellias get protection starting around 11am to 12pm but some Japonicas' leaves had a problem even with with that so I had to transplant them to get more shade. Camellia Sasanquas' leaves will do better in the sunlight department if you determine there is maybe too much sun near the fence in the summer. The Quarterly Camellia Journal suggests these sasanquas for places with lots of sun: Yuletide, Hugh Evans, Jean May, Bert Jones, Narumigata, Navajo, Double Rainbow, Yae-arare aka Double Hailstone, Setsugekka and Mine-no-yuki. Others from the hiemalis species are Bonanza, Kanjiro, Shishigashira and Dazzler.
Perhaps a way to grow both in the same place might be to plant the camellias close to the shaded area of the fence and the hibiscus in the more sunny area. It might be worth exploring that but you should do this closer to the summer when the sun comes down almost straight down and not an agle as it does now. I release beneficial insects to deal with spider mites in Hibiscus and Roses. The camellias do not suffer as much from this. Beneficial insects do not like to be in full sun so Hibiscus suffer more from spider mites than camellias do.
Similarities: My camellias and my Hibiscus (planted in part shade and sunny locales) both get water from the same drip irrigation source so watering should not be a problem. Just water when the soil feels almost dry.
I fertilize both somewhat similarly so this proved not to be an issue either. Lots of organic compost in Spring; some cottonseed meal about once a month thru July. Some sulphur to acidify my alkaline soil and some magnesium from Epmsom Salts. | 
