I don't know if I would really say combat in RE1 (1996) is "selective or avoidable"? (Re)Killing all the zombies makes exploring much, much easier, and you get enough ammo to blast through the whole game. I have heard that ammo was made tighter in later releases/remakes of the game, but I played the original PlayStation version last year (or specifically the Director's Cut version) and it seemed like it was basically always correct to clear each room as you encountered it.

I guess you could skip killing zombies, in the same way that you could play Super Mario Bros. without stomping on goombas, but it hardly ever felt like the right idea. Maybe the section in the basement where the zombies respawn like five times, although the fixed camera sort of makes it difficult to run past them in certain screen transitions.

I will also say I only played Jill's story, so maybe it's different for Chris.