Any recommendations on the best way to adhere dragees to a crusting cream cheese frosting which has been airbrushed? I have attached a photo of the cake the bride wants me to replicate.

Well the lowest 3 tiers are hand placed.  The top two probably are rolled in the smaller ones.  The dried/set icing is sprayed w/a very light mist of water OR covered in a light coat of piping gel, then the larger dragees are hand placed among/over the small ones.   To roll the cakes cover a cookie sheet w/the dragees and turn the cake on it's side rolling it through.  PLace the lgr ones using  tweezers by tuching the dragee into piping gel & place OR pipe a very smalldot of icing or melted choco where you want the dragee to go.

I use Tylose glue (Tylose and water, fairly thick consistency) for adhering pearls. 

Well Sandra, there is always more than one way to skin a cat!   (Or so the saying goes.)  Of course we all have learned that *MY* way isn't always the best way to do something.  What works for one person does not always for everyone else.    

I actually have never covered a cake in dragees (the are not legal in CA) but saw a t.v. show about that just a few days before.

Oh, I think piping gel is great!  I use Tylose glue because I always have it on hand and I don't necessarily always have piping gel.  I just added it as another option.   Personally, I don't think there is a wrong way, if it works.