Yes, you can use the decorations on top of fondant. You could even make little hills out of additional fondant and cover them with sanding sugar for sparkle.
-- Sugar Sugar by SSmiley
Personally I think making the mounds of snow would be easier with buttercream. If you make buttercream quite stiff, you can plop on top of the fondant. Then let icing sit for a bit, take a spoon or flat knife gently stir and pull up. Should leave peaks. I’ve then spread out royal icing in white and pale blue, let royal dry hard. Crush, the royal icing and sprinkle over mounds of buttercream snow. Gives a lovely snowy affect.
-- Creativity is God's gift to us. Using our creativity is our gift back to God. Clarky's Cakes 😎