How to use robot_localization /odometry/filtered

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So I have two robot_localization nodes setup. The first fuses the vehicle odometry and the imu data. The second will add in GPS and hector_slam pose estimates.

My question is, should I fuse the output of the first node (/odometry/filtered) into the second node or should I re-fuse the vehicle odometry and imu data? If the former, the second (map) robot_localization node never publishes anything if I fuse the output of the first directly. (Also, the navsat node doesn't work with the /odometry/filtered data either).

Here is a sample /odometry/filtered message (output from the first node).

header: 
  seq: 235
  stamp: 
    secs: 1455846048
    nsecs: 782704923
  frame_id: odom
child_frame_id: base_link
pose: 
  pose: 
    position: 
      x: 0.060692385786
      y: 8.51043448483e-06
      z: 0.0
    orientation: 
      x: 0.0
      y: 0.0
      z: 7.45214107357e-05
      w: 0.999999997223
  covariance: [0.39148006559512866, -1.0221015344746652e-08, 0.0, 0.0, 0.0, 7.160358808761269e-08, -1.0221015344746746e-08, 0.39152977031124553, 0.0, 0.0, 0.0, 6.453229401104118e-05, 0.0, 0.0, 3.332912064876806e-07, 1.341899911334871e-24, 5.233156817556127e-19, 0.0, 0.0, 0.0, 1.3418999113348712e-24, 3.3324912207294784e-07, -1.6669589116712293e-32, 0.0, 0.0, 0.0, 5.233156817556124e-19, -1.6669590914679116e-32, 3.3324912207294784e-07, 0.0, 7.160358808761269e-08, 6.453229401104114e-05, 0.0, 0.0, 0.0, 0.0773158946732772]
twist: 
  twist: 
    linear: 
      x: -0.000285365096838
      y: 0.0
      z: 0.0
    angular: 
      x: 0.0
      y: 0.0
      z: 5.54621444365e-05
  covariance: [0.0019138416154638686, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0019138416154638686, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 3.332701589929017e-07, 1.9950504214512513e-31, 1.2764323815697058e-27, 0.0, 0.0, 0.0, 1.9950504214512495e-31, 3.330812024673111e-07, -1.34664748772665e-39, 0.0, 0.0, 0.0, 1.276432381569705e-27, -1.5229681057398406e-38, 3.330812024673111e-07, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.04978277263316132]

And here is my localization launch file ...

<!-- Launch file for ekf_localization_node -->

<!-- Layer 1 Localization: Odometry Frame -->
<launch>
    <node pkg="tf" type="static_transform_publisher" name="tach_odom123" args="0 0 0 0 0 0 1 odom tach_odom 100" />
    <node pkg="rsl_rover" type="imu_overrid_covariance.py" name="IOC" />
    <!--    <node pkg="rsl_rover" type="virt_yaw_sensor.py" name="VirtYaw" output="screen"/> -->
    <node pkg="imu_complementary_filter" type="complementary_filter_node" name="complementary_filter_node" >
    <remap from="imu/data_raw" to="imu/data_cov" />
    <remap from="imu/mag" to="imu/mag" />
    <remap from="imu/data" to="imu/data_filtered" />
    <param name="do_bias_estimation" value="true"/>
    <param name="do_adaptive_gain" value="true"/>
    <param name="use_mag" value="false"/>
    <param name="gain_acc" value="0.01"/>
    <param name="gain_mag" value="0.01"/>
    </node>

    <node pkg="robot_localization" type="ekf_localization_node" name="odom_localization" clear_params="true" output="screen">

      <param name="frequency" value="30"/>
      <param name="sensor_timeout" value="0.1"/>
      <param name="two_d_mode" value="true"/>

      <param name="map_frame" value="map"/>
      <param name="odom_frame" value="odom"/>
      <param name="base_link_frame" value="base_link"/>
      <param name="world_frame" value="odom"/>

      <param name="transform_time_offset" value="0.0"/>

      <param name="odom0" value="/VehicleTach"/>
      <param name="imu0" value="imu/data_filtered"/>

      <rosparam param="odom0_config">[false, false, false,
                                      false, false, false,
                                      true,  true, false,
                                      false, false, false,
                                      false, false, false]</rosparam>

                  <!--      <rosparam param="odom1_config ...