From Index: Forces of the Astra Militarum:
The Manticore Battery does not have the 'Immobile' rule so there is no reason why you can't tow it.
I see the argument with the Hydra Battery and Earthshaker Battery though. They both have the 'Immobile' rule which says "This model cannot move for any reason...". This conflicts with the Centaur Light Carrier's 'Artillery Tractor' rule that allows it to move
<REGIMENT> ARTILERY models. My ruling is that you have to follow both rules, so 'immobile' models cannot be moved.
Luckily the Centair Light Carrier is an utterly pointless unit that no one would ever dream of taking, so this situation will never come up