That you would even use react.js in the first place is bad, using it just because you want to generate markup? Even worse -- particularly given the inaccessible non-semantic gibberish it has the tendency of vomiting up.
There's a reason things built with react (like this site) are a giant middle finger to accessibility, and why it's best restricted to crapplications, not websites... and really the only reason to server-side generate what react craps out would be building websites...
At which point just output semantic markup in a logical document order; I know, the horrors of actually having to understand what HTML is, how to use it, and how to develop for all users, not just the handful willing to stomach the scripttardery.