It should also probably be noted that Les Misérables was the product of the 1860s and that particular understanding of communism and socialism when applied to an 1830s setting, and not what we would think of communism or socialism in the modern sense.

In Enjolras’ case, he is a character just as much colored by the Republican movement of the 1789 Revolution as he is by the writings of Rousseau (although many of their number also idealized Rousseau). He (and other members of Les Amis, actually) are actually based to some extent on several key figures within that particular moment in the French Republican movement. 

Enjolras, in particular, is linked to Saint-Just at least once, as well as Saint-Just’s mentor and giant of the Revolution, Maximillien Robespierre. While Robespierre was undoubtedly a giant Rousseau fanboy, he could also be described as a communist of convenience. Sympathizing deeply with the poor, he believed that the people should be provided for in times of economic hardship regardless of who particularly owned the food, or necessary supplies. However, he also specifically assured remaining members of the aristocracy who converted to Republicanism in the midst of the Revolution (that phrasing isn’t a joke, Republicanism at that time had its own religion and could almost be described as cult as much as a system of government) that he “did not wish to touch their treasures, however impure their source may be.” Which, admittedly was a bit of a glib remark, but did ring true for his general policy.

Robespierre also idealized a the concept of a virtuous Republic, a concept which is definitely reflected in the character of Enjolras. However, while the traditional French Republican (again, circa the 1789 Revolution) belief in universal suffrage (even if in practical application it wasn’t so universal) and cult-like reverence for the power of the people would make me hard pressed to define him as a republican in the modern sense of United States politics, I certainly don’t think that necessarily defaults him to the other team. Robespierre and and his club (which was the going term for parties) started off as a small but radical group within the Estates General and later became the dominant force within the Convention, but they were extremists and radicals through and through (who… Also all idealized Rousseau.) I find it far more likely that he’d attach himself to some radical liberal party and fight for that (and the endangered species known as the voice of the people within a modern republic) instead of towing one party line or other.

However, on a rather glib note, I think Rousseau would be pretty chill with Socialist Republicanism so long as virtue and merit really were at the heart of it. And, you know, the voice of the people (who, by Rousseau’s writings would be educated and willing to perform their civic duty to the fullest and benefit of their fellow citizens regardless of their individual preferences) wasn’t lost within a giant state, bogged down by needless heirarchies that impersonalized the relationship between the people and their representatives.