I do this kind of work & Its dependant on a number of factors, but basiclly if its being moved by the company that owns it for the purposes of thier buisness & if they operate without the vehicles without the need for an operators licence then probably not, if any of the above is not met then yes.
But basiclly as far as the men at the ministry are concerned if your company do not need a operators licence then you probably do not need a tacho in the head, but that will need a prosecution to confirm it one way or the other.
Everyone I know uses a tacho on this kind of work as it keeps you totally legal & makes life a lot simpler when the law stops you. It also stops the pressure of you need to be there by…, can you just… etc.etc.
Incidently I do work for rental companys/dealerships.