By that definition, we can also detect the weak interaction by feeling the sun on our face or the warmth of radioactive material.
But I still suspect we would be able to sense gravity without inner ear fluid, even if only slightly. When we vigorously shake our head, the fluid flows against the hairs, so naturally the electromagnetic force and/or Pauli exclusion is mostly responsible for sensing. However, even absent any inner ear fluid, the hairs should still bend due to gravity -- I just don't know how appreciable the effect is.
Not sure why the organ doing the sensing matters. I'm talking about thermoreceptors in the skin, obviously.
But just to be clear, I'm saying that you're actually sensing electromagnetic force in your inner ear _caused by_ gravity. Not gravity itself.
Even if the hairs bend due to gravity alone, that force upon the sensory receptors is an electromagnetic one.
But if you consider that 'direct' then you must also consider sensing of the weak force, as 'direct'. Whether it be via thermoreceptors or your retina.
tldr
gravity : bending hairs :: weak interaction : radium glow