React.js: Is it possible to convert a react component to HTML DOM’s?

You can render a ReactElement in a detached DOM Node via React.render. Thus, the following code should work for you.

createMarker: function() {

  /** Some other lines of code */

  _this = this;

  google.maps.event.addListener(marker, 'click', function() {

    var div = document.createElement('div');
    ReactDOM.render( _this._renderInfoWindow(place), div );
    infowindow.setContent( div );
    infowindow.open(map, this);

  });

},