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This should not affect the water absorption of your dogwood. In fact, it may actually help conserve water, provided you are not placing a plastic barrier beneath the rocks. You should also consider keeping the rocks at least a couple inches away from the tree itself. I know you said nothing grows here, but in the event of any grass or weeds, you could choose to place your rocks on landscape fabric, which not only allows for air flow and water to pass through but eliminates weed growth.

It should recover on its own, though you probably won't have any blooms this year. The following articles should be of some help to you:
https://www.gardeningknowhow.com/ornamental/trees/dogwood/caring-dogwood-trees.htm
https://www.gardeningknowhow.com/plant-problems/pests/deer/how-to-protect-trees-from-deer.htm

It sounds like they have too much nitrogen. Add a phosphorus rich fertilizer to them to get them blooming again. This article will have other suggestions as well: https://www.gardeningknowhow.com/ornamental/trees/dogwood/dogwood-tree-not-flowering.htm

Trees need to be mature before they can flower. As this a young dogwood, I would give it at least another year before expecting blooms. They take about 3-4 years before they are of a blooming age.

It sounds like they have too much nitrogen. Add a phosphorus rich fertilizer to them to get them blooming again. This article will have other suggestions as well: https://www.gardeningknowhow.com/ornamental/trees/dogwood/dogwood-tree-not-flowering.htm

Unusually cold weather could have damaged the trees and subsequent buds. Generally, if the trees survived, they will slowly recover, though blooming may not occur this season. This article should help determine whether your trees are still alive: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm