Although the Scourge never reappear in the series, they are mentioned as one of the groups who may pose a threat to Connor's existence in Dad (2001), shortly after his birth.
This is the first appearance of Sean Gunn in the this season. In this episode, he appears briefly as a demon named Lucas. Later in the season, in She (2000) he appears as a character named Mars.
The Scourge are reminiscent of the Nazi Party in Germany, who believed that pure races, specifically the Aryan race, were superior. To protect their purity, they persecuted the Jews like the Scourge persecute half-demons. Their uniforms too are similar as is the way that Angel styles his hair whilst undercover.
It takes a surprisingly long time to teach a group of civilians to march in step; time you don't have for nameless extras on a tv show. Note that when the Scourge troops are marching ominously down the street they are not even close to being in step although the sound is of perfect double time marching.
The murderous Drill Sergeant demon who tries to break Buffy's spirit in Anne (1998) appears identical to the "football head" pure-blooded soldiers in this company of The Scourge.