Yes rhodos. are shallow rooted plants, possibly because they originated in forested areas and the deeper soil was full of tree roots. It isn't that you plant them shallowly but that they have roots that only go a short depth into the soil. In addition rhodo. roots are very fine and it takes them a long while to grow into the surrounding soil so you need to keep the rootball well watered and mulch around the shrub. Try not to dig around them as this will disturb and damage the roots.

also with being forrest dwellers there surface roots catch the water that forms as dew. deeper roots go down for water more in the water table. a good evolutionary strategy.