The skull known as the 'Totenkopf' was re-adopted by the Nazi Julius Schreck who led Hitler's personal SS bodyguard division called Stabswach as the groups official insignia. It was later adopted by some Panzer divisions and more infamously the SS-Totenkopfverbände who were responsible for the administration of the concentration and death camps. The skull itself has been around for many years so it was incorporated by Hugo Boss as opposed to being part of their design. The lightning bolts on the other hand are just a stylised way of writing SS short for Schutzstaffel which was a Nazi military group (note Nazi as opposed to German - they fought for National Socialism as opposed to Germany which allowed for Sikh SS divisions) literally meaning Protection Squad but they took part in conventional war as well as the holocaust. So to answer your question, Hugo Boss which was a Nazi supporter would have had to incorporate those symbols not because of their spookiness but because they help to denote which unit the soldier is of.

Edit: Also most SS officers had the Skull on their uniforms including the likes of the Waffen SS and Allgemeine SS officers.