Yes, the behavior you're experiencing with SkeletonGraphic not applying custom slot materials as expected is consistent with the limitations of SkeletonGraphic in the Spine-Unity runtime. As mentioned in the provided contexts, SkeletonGraphic has structural limitations that prevent it from supporting custom slot materials directly, unlike SkeletonAnimation which can handle custom materials more flexibly.
The SkeletonGraphicCustomMaterials component is indeed a workaround for applying custom materials to SkeletonGraphic, but it has its limitations and does not support custom slot materials as powerfully as SkeletonRendererCustomMaterials does for SkeletonAnimation. This is due to the inherent limitations of SkeletonGraphic, including the single atlas texture limitation and the inability to support multiple submeshes or materials, as highlighted in the contexts.
The issue you referenced (EsotericSoftware/spine-runtimesissues/1982) might be related if it discusses limitations or bugs affecting material handling in SkeletonGraphic. For now, using SkeletonGraphicCustomMaterials with its limitations or switching to SkeletonAnimation for more complex material customizations are the primary workarounds.