All the default shaders support deferred and forward rendering. If a custom shader says "pragma surface" then it will support both as well. If it says "pragma vert" or "pragma frag" then it might or might not. But even if you have deferred rendering enabled, a shader that is only compatible with forward rendering will…
With surface shaders, anything with a lighting function suffixed with _Prepass will render using deferred rendering. With vert/frag shaders there's any pass using #pragma multicompile _something_ but I'm not sure what it is.