The 5th edition rulebook specifically states models with Tau jetpacks are also relentless. This allows them to move and fire heavy weapons on the move like bikes and terminators. This is an upgrade from 4th edition. Note, however, broadside suits do not have jet packs. Also note that crisis suits and stealth troops do not have many heavy choices.
Even if the above were not true, (which it is) the FAQ specifically states that the marker light drone for stealth and crisis suits works on the move. The explanation given in my previous post was an attempt to explain the logic behind that ruling and the ruling that units equipped the the stabilization upgrade who have drones cannot move and fire marker lights.