Thanks for the elaborations @rmerriam! For step/leg motion types that are more complicated, arbitrary motions can be executed with EndEffectorTrajectory.msg from free_gait_msgs:
# Definition of a trajectory for the foot.
# Leg name ('LF_LEG', 'RH_LEG' etc.).
string name
# Trajectory for the end effector.
# Trajectory can contain transforms, twists, or accelerations,
# or combinations of these.
trajectory_msgs/MultiDOFJointTrajectory trajectory
# Target surface normal.
# Leave empty of no contact is expected or not known.
geometry_msgs/Vector3Stamped surface_normal
# If contact of the end effector should be ignored.
# Default is false.
bool ignore_contact
# If pose adaptation should ignore this leg motion.
# Default is false.
bool ignore_for_pose_adaptation