The material is a standard UE4 material, you can use any material you want as long as you add a texture node to it that is named a special name, the system will look for that input and set the texture input by that name. You can look at the materials supplied in the SDK (they are very basic and easy) to look at the input exactly. You can scale and modify the UV’s, just keep in mind that UV warping on the GPU isn’t reflect in the input side of things: the UV coordinates on static meshes are used to figure out input location on world actors, so material specific UV effects can be done as long as you aren’t trying to interact with the object OR your UV warping is minor enough not to cause oddities on input (like a mild warping or sine wave would be fine).
I have not ever used Coherent UI however it supports more platforms than Radiant (Mac, Linux, Mobile) but it significantly more expensive. I’ve been told by a number of licensees who have evaluated both that RadiantUI is superior (more feature rich, easier to use): edover (posted above)
RadiantUI input systems “just work” automatically, it supports interaction with any kind of UV’ed static mesh (which is a unique feature of RadiantUI). RadiantUI also comes with source code, but is currently confined to Windows 7. I intend to support Mac and Linux but I have no time table right now. 's WebUI is a free solution but lacks the same polish and feature set (however it is free, comes with source code, and may support more platforms).