First, the soil should be tested for drainage. A lack of good drainage is the major cause for demise of rhododendrons. They get root rot if the roots remain too wet in hot weather. This is almost always a fatal disease. If drainage is a problem, then a raised bed is normally the best alternative.

Then, the sphagnum moss should have been incorporated with the soil. It is a soil amendment, not an alternate soil. Today, pine bark is preferred by many to sphagnum moss, especially on the West Coast.

The root balls should have been opened up before they were planting. This prevents the roots from strangling each other and helps them establish themselves in the soil.

Then, they should have been well mulched. If all of this was done, then being a little loose would not be a concern.

Here is a link that might be useful: How to grow rhododendrons and azaleas.