This is Christophe Riccio's categorization of all GLSL types; you'll see this in the forthcoming book OpenGL Insights.

vert in varying frag out uniform scalar ✔ ✔ ✔ ✔ vector ✔ ✔ ✔ ✔ matrix ✔ ✔ ✖ ✔ array ✔ ✔ ✔ ✔ structure ✖ ✔ ✖ ✔ samplers ✖ ✖ ✖ ✔ images ✖ ✖ ✖ ✔ atomic counters ✖ ✖ ✖ ✔ block ✖ ✔ ✖ ✔