Not in this implementation.
These decals generate no additional draw calls.
If you have 1 decal in the scene - the number of draw calls will be the same as if you had 0.
If you have 1000 decals - it will still be 0 draw calls. If you have 100,000 decals - still the same.
The technique is called “clustered decals”, and in meep it’s part of the forward+ rendering pipeline.
It’s important to contrast this with how decals work in three.js. Three.js offers a decal implementation using clipped geometry, which is a completely different technique. A much simpler technique. It cuts a piece of underlying geometry, applies new set of UVs to it, and marks it with vertexOffset, to draw on top of other geometry in the scene. This is why you have to re-generate the decal every time the mesh changes or moves to a new spot where a different set of meshes overlap with the decal bounds.