Not fully sure if this is is what you need, but Daniel Stonier sent me this example of an ecto cell with internal ros publisher :

/**
 * @file /dslam_ecto_bridge/src/dslam_viz/rviz_relay.cpp
 * 
 * @brief Short description of this file.
 **/
/*****************************************************************************
** Includes
*****************************************************************************/

#include <dslam_central/statistics.hpp>
#include <dslam_msgs/Map.h>
#include <ecto/ecto.hpp>
#include <iostream>
#include <memory>
#include <ros/ros.h>
#include <string>

/*****************************************************************************
** Namespaces
*****************************************************************************/

namespace dslam_ecto_bridge {
namespace cells {

/*****************************************************************************
 ** Cell
 *****************************************************************************/

struct RVizRelay
{
  RVizRelay()
   : throttle_counter(1)
  {}

  static void declare_params(ecto::tendrils& params)
  {
    params.declare<unsigned int>(&RVizRelay::every_n_,
                         "every_n",
                         "Throttle publishing to only 1 in every n executions.",
                         1
                         );
  }

  static void
  declare_io(const ecto::tendrils& params, ecto::tendrils& in, ecto::tendrils& out)
  {
//    in.declare<dslam_viewer::StereoParameters>("stereo_parameters", "Structure containing all the stereo parameters.");
    in.declare<dslam_central::Statistics>(&RVizRelay::statistics_,  "statistics", "DamnSlam tracker-mapper statistics.");
  }

  void configure(const ecto::tendrils& params, const ecto::tendrils& in, const ecto::tendrils& out)
  {
    ros::NodeHandle nh("~");
    nh.param<std::string>("global_frame_id", global_frame_id, "dslam_map");
    dslam_keyframes_publisher = nh.advertise<dslam_msgs::Map>("keyframes", 5, true);
    //    stereo_parameters = in.get<dslam_viewer::StereoParameters>("stereo_parameters");
  }

  int process(const ecto::tendrils& in, const ecto::tendrils& out)
  {
    // we actually want to publish every time we get a frame update
//    int num_subscribers = dslam_keyframes_publisher.getNumSubscribers();
//    if ( num_subscribers != 0 && throttle_counter == *every_n_) {
      for ( const auto &keyframe_statistics : statistics_->keyframe_statistics_queue ) {
        dslam_msgs::Map msg;
        msg.header.stamp = ros::Time::now();
        msg.header.frame_id = global_frame_id;
        for (const auto& id_keyframe_pair : keyframe_statistics->frames) {
          dslam_msgs::KeyFrame msg_keyframe;
          msg_keyframe.id = id_keyframe_pair.second.id;
          msg_keyframe.transform.translation.x = id_keyframe_pair.second.T_keyframe_rel_map.translation().x();
          msg_keyframe.transform.translation.y = id_keyframe_pair.second.T_keyframe_rel_map.translation().y();
          msg_keyframe.transform.translation.z = id_keyframe_pair.second.T_keyframe_rel_map.translation().z();
          msg_keyframe.transform.rotation.x = id_keyframe_pair.second.T_keyframe_rel_map.unit_quaternion().x();
          msg_keyframe.transform.rotation.y = id_keyframe_pair.second.T_keyframe_rel_map.unit_quaternion().y();
          msg_keyframe.transform.rotation.z = id_keyframe_pair.second.T_keyframe_rel_map.unit_quaternion().z();
          msg_keyframe.transform.rotation.w = id_keyframe_pair.second.T_keyframe_rel_map.unit_quaternion().w();
          msg.keyframes.push_back(msg_keyframe);
        }
        for (const auto& edge : keyframe_statistics->edges) {
          dslam_msgs::Edge msg_edge;
          msg_edge.begin = edge.first;
          msg_edge.end = edge.second;
          msg.edges.push_back(msg_edge);
        }
        dslam_keyframes_publisher.publish(msg);
      }
//    }
    throttle_counter = ( throttle_counter == *every_n_) ? 1 : throttle_counter + 1;
    return ecto::OK;
  }

private:
  // variables
  ros::Publisher dslam_keyframes_publisher;
  unsigned int throttle_counter;
  std::string global_frame_id;
  // param tendrils
  ecto::spore<unsigned int> every_n_;
  // input tendrils
  ecto::spore<dslam_central::Statistics> statistics_;
};

} // namespace cells
} // namespace dslam_ecto_bridge

// This macro is required to register the cell with the module
// first argument: the module that it is to be part of
// second argument: the cell we want to expose in the module
// third argument: the name of that cell as seen in Python
// fourth argument: a description of what that cell does
ECTO_CELL(dslam_viz, dslam_ecto_bridge::cells::RVizRelay, "RVizRelay", "Relays data to the dslam rviz plugin.");