Good question, actually!
I think I mostly see Rockford as some sort of abstract player sprite (which in fact is just what he is), just like in many of those old C64 games where there were only around 16x16 pixels for the player figure (or even only 8x16, with horizontally wider pixels), never thinking too much about it. (Rockford in the classic game has a width of 6 (wide) pixels and a height of 15 (normal) pixels.)
But this is indeed interesting. For example, with Emerald Mine or Supaplex, there were 16x16 pixels (with a few more colors), which was just enough detail to see clearly that this is a little guy or a pac-man like figure. Rockford, on the other hand, has just a little bit less details, but which allows for more room for your own imagination. Maybe this is his "secret".
So, indeed, I also see Rockford as something like an ant or insect (but with four legs), especially when seen from the side.