I used a Reese hitch WD (chains style) for years and had a friction sway bar. Yes, you do have to drill holes in the frame. Never had a sway problem that I'm aware of and towed with it on and without it. I did notice a difference on interstate driving, especially when big-rig trucks pass.
Now, I've got the Equal-i-zer WD hitch system. It's suppose to have built-in sway control. Either I have no sway or it's working, because to date, I've not had any sway.