In Scaramouche, Moreau goes around instigating uproar against the French government. The novel is historical fiction but what are the similarities between Sabatini's portrayal of the start of the French revolution, with small groups of activist getting the wheels turning on the revolution, to the actual causes of the revolution.
You are right in pointing to the significance of the French Revolution as much more than a neutral backdrop to this story. Sabatini's desire to have government be a meritocracy rather than a plutocracy or aristocracy is very much exemplified by the themes of this historic period. Sabatini was also a very careful historical researcher and made sure to accurately portray many details of his historic period.
The actual causes of the Revolution were primarily economic: the king had practically bankrupted the country with his extravagant spending and his involvement in the American Revolution. Due to poor harvests, food was scarce and the lower classes were going hungry. The political unrest in the novel is indeed a reflection of historic fact.
The National Assembly in Scaramouche is also an accurate historical fact: this was a body created by the Third Estate in order to create a constitution that allowed the voices of the majority to be heard. Given the power of the Third Estate (it represented 98 percent of the people), some members of the nobility and the clergy soon jointed, and the king had no choice but to recognize this new Assembly and allow it to continue its deliberations.
As for your question regarding small groups of activists, this is also correct. Many of the rebellions during this time period were instigated by mobs, rioters, and small groups of insurgents. The National Assembly was not a unified group by any means, and the presence of factions (Girondins, Montagnards, Jacobins, Cordeliers) testifies to the presence of various influential groups. The violent chaos instigated by these groups (and the excesses of the Jacobins, who eventually seized the National Convention) were what ultimately led to the end of the French Revolution with Napoleon's coup d'etat.