I have only experience with dear-imgui so far (mentioned in the readme), but nuklear should be very similar in its requirements. You basically just need a GL context (or other 3D APIs equivalent) to write a wrapper for, SDL is sort of overkill for this.
In my case I integrated imgui with my "weekend engine" Oryol, which has a very slim wrapper around 3D APIs, and I have this running in WebGL (via emscripten) and GLES2 on Raspberry Pi 2 (should also work on the original Pi). The resulting executables are small enough for most 32-bit embedded platforms (a couple hundred KBytes), and have a much shorter list of system dependencies. On Raspberry Pi it doesn't even need a window system, it runs straight from the Linux terminal and uses the Pi's EGL wrapper.
In my case I integrated imgui with my "weekend engine" Oryol, which has a very slim wrapper around 3D APIs, and I have this running in WebGL (via emscripten) and GLES2 on Raspberry Pi 2 (should also work on the original Pi). The resulting executables are small enough for most 32-bit embedded platforms (a couple hundred KBytes), and have a much shorter list of system dependencies. On Raspberry Pi it doesn't even need a window system, it runs straight from the Linux terminal and uses the Pi's EGL wrapper.
For instance here's the WebGL imgui demo (325 kByte): http://floooh.github.io/oryol/asmjs/ImGuiDemo.html