Can I plant a Viburnum lentago (Nannyberry Viburnum) [or Amelanchier canadensis, for that matter] on a shallow-soil location that has only 9" soil above the bed rock? I live in zone 6b and I'm concerned that the roots will not be deep enough to escape the freezing temperatures that can temporarily dip down to around 5 bellow 0 F.

Would this be an acceptable situation for a viburnum?

(I'm actually going to plant two of these right next to eachother so that they insculate [bond], forming a mutually fertilizing pair).