they can be pruned like that but it would not be my preference for a sheared shrub. some people treat azaleas this way in my area and it just looks odd to me to see a squared-off hedge of azalea but....to each his own.
the site sounds good for sun exposure but i would also suggest that a bed surrounded by concrete might not be perfect for an acid loving shrub. many times, foundation plantings can become chlorotic looking from the lime leaching into the soil.
mature camellias will be expensive and small plants will take a long time to reach the width and height you may want to provide screening.
the area might be better suited to a different plant for a hedge.
so, the bed itself is about 4' wide but the plants can grow over the bed boundary to 15' wide?

I agree, you need shrubs, vines or upright growing trees that grow well in more of an alkaline type soil, since so much lime will be leaching from the driveway and retaining wall.

I have seen it reported that some people have gotten a Climbing Fig (Ficus Pumila) to grow in USDA Zone 5. That is hard for me believe, since most sites list it as a 10-11 zone vine. But since the reports are not consistant, you might research your area to see if they would grow in your zone 8. They are reported to do fine in moist well draining organic soils with PH level ranges from 5.5 to 7.5

You could also consider growing the evergreen twining vine, Coral or Red honey suckle (Lonicera sempervirens)that blooms in late summer. It is a fast grower, but not as vigorus of a grower as the the common honeysuckle; thus, it is not a pest.

If you desire to plant a row of small trees,
You could consider planting the Wax Myrtle (myrica cerifera)evergreen trees. This tree is a fast grower that you could prune to form leggy trunks. Then you could underplant them with ground covers like the evergreen creeping phlox cultivars, or underplant them with a ground coverage planting of Liriope Muscari.