The Nemesis all drop two versions of shoulders, each with different + skills on them. The stats on the shoulders usually match the skills they give bonuses to. IE, Iron Maiden has Cadence shoulders with phys and int trauma
Yes, each drop 2 kinds of shoulders, and you 100% get one with each Nemesis kill (unlike most MI, that dont have 100% droprate). They all have nice stats, but some arent so useful because legendary shoulder will be simply better for certain builds.