hard vang means no topping lift?
In most cases you can eliminate the need for a topping lift when you go to a rigid vang, but there will be times when you will want to rig the main halyard as a topping lift. Most boats end up using the main halyard as a topping lift once the mainsail has been dropped in order to keep the boom from bouncing around too violently.
As to the connection between a full batten mainsail and a rigid vang, there is none at all. Now then, if you are talking about using a full roached sail with full length battens, then the real problem is more likely to be the backstay rather than the topping lift.