For the Hattery, I treat the masks the same as the diffuse and normal maps. I assume they have gamma premultiplied into them. Otherwise the colors appear too bright/vibrant/saturated.
It is highly unlikely that they actually use gamma correction as the dota materials do not use physically based shading (for example the diffuse texture has shadows already premultiplied => not albedo) therefore using the linear gamma workflow would just take more processing time for no real reason. BTW using it only for…