You don't need to dimple the barrel anyway. That dimple is there to make it easier to get your gas block located correctly. If the set screw goes in the dimple, then the gas port in the gas block MUST be centered over the gas port in the barrel and there is no need to measure distances and shim the gas block while tightening it down. There is also no need to eyeball the GB to TDC. That is all the dimples do. If you really think the dimples will make the gas block less likely to rotate, you are kidding yourself. I have set screw gas blocks on all kinds of ARs in all kinds of calibers and only recently were any of them dimpled. I will put you dollars to doughnuts, you tighten down the set screw like you have a pair but not to the point of stripping and it is not going anywhere, dimple or not. But dimpling is great if for no other reason than for alignment and removal ease.
When you do tighten down the set screw types, if there is no dimple or the dimple is too small, it throws up a burr on the barrel and that can make removal later on a twist and cuss ordeal. I really do think the dimpling helps prevent that burr from making the gas block hard to take off later and that is another plus for dimpling, and would be the only reason to dimple the second set screw.
Personally, I prefer the clamp on like the VLTOR, YHM, or Lo-Pro DD. DD now makes a clamp on similar to the VLTOR and YHM and all three of them are great. They are very snug on the barrel so you must spread it a bit to get it on but that is a no-brainer. Put the clamp screw in from the other side, put a penny in there to butt the screw up against and tighten it down slightly to spread the clamp apart, then it slides right on. Loosen the screw, rotate to align, and tighten down. The DD and VLTRO clamp on you can use the hole in the bottom of the gas block to align with the dimple, if your barrel has one, and that will help you align it if you don't want to use calipers and feeler gauges and eye-balls to get it all aligned down to the .001 of an inch, which is NOT necessary.