Looking to cover a middle tier of a cake in edible crystals and i'm looking for some recommendations as I'd like to have a swiss meringue base for attaching the crystals, like the cake in the picture.

Also would the crystals melt on swiss meringue?

It looks like sparkling sugar.  Since the cake will require refrigeration because of the frosting, the sugar should be applied as close to delivery/set up/serving time as possible. Even if it's not drawing moisture from icing, it will draw it from the air.