Yes,
You can force only 3DoF (x,y and yaw) registrations:
<node pkg="rtabmap_ros" type="rgbd_odometry" name="rgbd_odometry">
<!-- Version 0.11 -->
<param name="Reg/Force3DoF" type="string" value="true"/>
<!-- Version 0.10 -->
<param name="Odom/Force2D" type="string" value="true"/>
</node>
<node pkg="rtabmap_ros" type="rtabmap" name="rtabmap">
<!-- Version 0.11 -->
<param name="Reg/Force3DoF" type="string" value="true"/>
<param name="Optimizer/Slam2D" type="string" value="true"/>
<!-- Version 0.10 -->
<param name="LccBow/Force2D" type="string" value="true"/>
<param name="RGBD/OptimizeSlam2D" type="string" value="true"/>
</node>
EDIT: Added graph optimization limited to 3DoF too.
cheers