In general, the skeleton components just generate a Mesh and render it using a standard MeshRenderer, so you can use whatever shader you want, just be sure to disable Advanced - PMA Vertex Colors at the component and export using straight alpha worflow if your shader does not support premultiplied-alpha textures. Alternatively, you could adjust your thirdparty shader or shader graph to support PMA textures. If you need more information on using shader graph with Spine, please briefly search the forum, this has been covered here on the forum before.
Regarding the officially provided shaders that come with the spine-unity runtime and the Spine URP Shaders UPM package: The Sprite shaders like Universal Render Pipeline/Spine/Sprite already provide a separate emission map channel, just use it in combination with a standard URP Bloom post processing effect as shown in the following screenshot:
