The guys on the towers were no problem. My Varmint rifle was out of ammo by that point. And Gecko Steak does not heal limb damage on hardcoe. Limb damage accumulates until you see a doctor or use a doctor's bag. So when four guys come barelling out of the door at you, you can't kill them all before a couple get a shot off. I'm usually able to kill one or two before they can hit me. Toss in a third and fourth and I'll take some damage and need to spend time reloading to kill them all.
Thanks for the explanation on how limb damage works but I do know

It sounds like your problem was any or all of the following:
1) You ran out of ammo.... I hope you meant you were reloading but the fact you got swarmed by multiple guys after suggest that is not the case. They should have never swarmed you if you were sniping properly because they would have never seen you. Get on a farther higher rock I guess lol... I sniped more than just the guard towers from a single position including the named guy standing out front. None of these fired a single shot before they died. Don't just start spam firing your rifle, wait for a headshot when you are hidden. Take it. If you hit, great, wait until you are hidden again. If you miss, wait until you are hidden again. If you see them coming dangerously close to your area, MOVE. Rare you have to worry that much but just giving you a checklist since you found this challenging. You should never have 4 guys "barreling" at you or you arent doing a very good job of sniping. You can also see the guys in the courtyard from many vantage points.
2) You went in to a raid with limb damage? I dunno why you would do that hopefully you just meant those were the injuries you got during the fight. Again the only time you should have been close is after you cleared half anyway.
3) After the above is done properly you can just walk in the front door and clean up stragglers. When you walk into the sub-buildings you just start opening fire (i was crouched and suprised myself but could still react before any damage was sustained) with your 9mm or shotgun and they will start to panic a bit. Yes they are shooting at you, but it's also a relatively small space with a handful of guys who are equally suprised so it's not a hit squad or anything. Run near some makeshift cover (i just ran over by the bar to avoid taking every bullet) and that's all you have to do (and aim your gun). I didn't use VATS for any of this raid so it's not that hard.
If you think you will be overwhelmed that seriously setup some mines or use a grenade to help you, but if that is your problem more often than not, you should recheck your strategies. I often employ the mine strategy with huge packs of mutated creatures and lure them into the trap.
I'm playing on hardcoe also and have only gotten limb damage twice, both times by a mutated creature and not a NPC. NPCs are very easily outsmarted and outmanuevered. Deathclaw not so much (although you can still apply the mine tactic to them and then they are slow as turtles heh)
Best of luck in future firefights!