The hot shot nipple is nothing more then a stainless steel conventional #11 nipple. Some have a longer nose and because of the metals used they last longer and don't seem to mark up as fast under the hammer. Also, they have a small hole drilled in their side which is meant to release gas from the ignition enough to split the cap open. So it is easier to remove. In some cases, it will remove itself when fired. One reason you have to check the nose of the hammer on occasion because it will pick them spent caps up and if you let a build up of spent caps gather in the hammer nose it can cause a misfire.
The musket cap nipple because of the wings on the top hat, don't need that hole to split them. Spent musket caps tend to come off very easy.
And its still the idea of a musket caps sends more flame into the fire channel then a #11 cap. Not necessarily a hotter flame, but larger volume of flame. So in some rifles it seems to make ignition more of a sure thing. But to be honest, I seldom have ignition problems with a properly prepared rifle and a #11 ignition system.