Dash does not natively support Material Edit and Blending for custom textures yet. And the reason for this is that we need to create custom master materials for each library we have support for. And it's very hard to create a Master Material that works well for any assets/materials.
That said, on of our users, Nehon, has created a small plugin that helps you use one of our Master Materials on your own assets, and thus gives you access to Material Edit and Blending for your custom assets.
It ain't perfect and won't work for any meshes/materials, but it is really cool, and from my testing it works surprisingly well! So feel free to give it a try, but of course, we can't guarantee any specific results, so use it with caution.