Nope. You can fight them just fine really, once you get the hang of it, and learn how to fight without locking on. They're hard to see, but they're not invincible or anything.
The enemies themselves are basically NPC player phantoms which, as far as I can tell, are basically wearing knight/elite knight armor and equipped with a longsword and a dagger, though they can swap out the offhand dagger for a crossbow to plink at you. They can also guard break and are very happy to do so, so don't turtle up at them or they'll crush your shield and crit your face. Best strat as far as I can tell is to swing at them as they're coming in, or to backstep out of the way of their first attack and punish afterward.
Or, as I mentioned, you can follow the left wall and avoid them altogether. There are a few nice items to be found on the right side, but nothing you can't live without. (The Old Sun Ring is probably the best thing in the fog woods - it's a ring that occasionally causes a fiery explosion around you when you get hit, preventing lockdown by enemies and doing some free fire damage to anyone that sticks around after hitting you, but it's more useful for pvp than pve.)