Provided you don’t rely on third party plugins such as Human, in R7 you can use Python or C# to create materials or the quite limited “create material” which is mostly just based around a simple shader that intakes color, emissivity, glossiness, etc. but nothing special in terms of no texture mapping or actual textures present.
In R8 there are now “Model Materials” which allow you to set many more properties of and create materials directly in GH and these can get baked into the objects/document with the new Bake Content component. However, at this time, UV mapping and texture inputs are not directly set with these nodes, you can however, query existing Rhino materials that have all the maps set up and then apply said materials to your objects so thats pretty awesome!! I think it would be possible to extend this by having a script query into the Rhino linked material user/default libraries and import from there but I haven’t messed around with that.
This thread is one example that gets into PBR material creation via scripting in GH and may or may not be worth your time to read but sharing in case: