I'm currently out and haven't had a chance to properly look at this, but, how does this interact with resource arrays?
Resource arrays should work as long as they're not dynamically indexed. (And the ps_5_1 test exercises that path.) Dynamic indexing of resource arrays can't work with combined samplers; there's essentially no way to create the required combined samplers in either the OpenGL or Vulkan APIs, and it's not clear what that would even look like.
There's perhaps an unresolved question of how to handle that if we do run into it in the scanner. The current behaviour is to return the base index for such accesses; an argument could be made for either not recording them at all, or e.g. setting some flag in the vkd3d_shader_combined_resource_sampler_info structure to indicate dynamic indexing is involved. Ultimately such shaders just aren't going to be usable with combined samplers though.