Both the Spine Editor and the spine-unity runtime support linear blending. Please note that the effect of blending in linear space is simply different by definition. LinearToGamma(GammaToLinear(color1) + GammaToLinear(color2)) is dramatically different than color1 + color2.
In the Spine Editor you can change the Spine Settings under Application - General Color Management from Gamma space to Linear space to see the actual blending result.
http://zh.esotericsoftware.com/spine-settings#%E8%89%B2%E5%BD%A9%E7%AE%A1%E7%90%86
(English link: http://esotericsoftware.com/spine-settings#Color-management)
Regarding the questions in the heading:
雨之师 spine是不是可以兼容自定义材质（类似shader），和hdr颜色
You can use custom shaders and materials with Spine skeletons. See the documentation section here:
https://esotericsoftware.com/spine-unity#Shader-Graph
You should then export with Straight Alpha workflow and at the SkeletonAnimation component want to disable Advanced - PMA Vertex Color unless your custom shaders can handle PMA textures and vertex colors.
The question is what do you expect from using different shaders? The Spine Shaders already perform correct Gamma to Linear space color transformations, the only current limitations are the following: HDR colors (e.g. white with intensity 2.0) for Material parameters or slot colors are currently not supported, only normal LDR colors in the range of [0.0 - 1.0].
