Yes - to both the questions I think actually. If I have understood it correctly, a fragment shader always needs a vertex shader to display anything (at least in Vuo). My guess is that the vertex shader is just a very basic quad and some default uniforms that sets up a framework for less boilerplate coding.
At the risk of confusing you further, if you look at the code for a custom GLSL image filter node in the Vuo source (that is the C source, has nothing to do with the shader editor), you can find the following line setting up the shader:
Oh, I see it working by running it in the shader editor (like a composition). Time and resolution are supported without declaring any uniforms. If you use the Image filter protocol/editor there is also provided an image of a bird when you run it standalone.
The code above is the only thing you need to input for a simple shader utilizing time, resolution and inputs. It will modulate the red channel by time, the green channel by the rendered window size, and the blue channel by a published port/slider.