It use to be possible with the online (and stand alone) DAE to GLTF converter to omit the texture files (not drop them with the DAE file) in order to simply keep the URI reference to the texture in the GLTF (or GLB) file.
At that time, doing this would throw and error message but the file was converted none the less.
It was then possible to upload the texture file next to the GLTF (or GLB) file and Cesium would load the texture on demand.
This allowed to share a single texture file across several models: very handy and weight saving!
Sadly, this is not possible anymore: if the texture file is not dropped along with the DAE file, the online converter throws a meaningless error (500 Internal Server Error) and nothing comes out of it.
It is part of the glTF specs to be able to reference a texture with a URI.
I could not try this with the recent stand-alone converter as the binaries are not available any more.