I would take it to mean "simple, hard-working people." However, "sedulous" could be a mistake for "seditionist," in which case it would mean something more like "violent, rebellious people." In any case, to call a group of people "a [something] lot" sounds a bit patronizing. It's typical of how an upper-class writer might describe a working-class group.
I think I recognize this particular phrase, but I don't remember where I've heard it before.
Spirillist gave a very good answer, I think, but I'll add that it's neither a cultural reference nor an expression, as far as I know. Please provide the context (the complete sentence, some information about the surrounding text.) Thanks!
"Rough and sedulous lot" is more likely meant in a humorous rather than patronising or derogatory way. In any case, the description fits a much broader public than working-class groups: 19th c. posses, organised criminals, a team of rescue workers, to name a few. The common requirements are rough looks and/or manners and a fierce devotion to the task at hand.