On a hollow bottom projectile if you really feel the need to put something under it, I would go with a sub base made by MMP although people will tell you that the sub base is only necessary when shooting large charges under a sabot. I've tried sub bases under some conicals and the difference in accuracy was not all the pronounced, so I stopped using them there.

In a hollow bottom, you want that base to expand as even as possible. If you had a wad of some sorts, the ignition of the powder might drive the wad up into the base of the projectile making it expand into the rifling in strange ways. I simply put a dab of lube in them. That lube will protect the bottom of the conical from the heat of the igniton.

On a flat based conical like the BullShop or the No Excuse, then the wad will help stabalize the pressure under the conical from the igniton and protect the bottom of the projectile from the ignition blast. Although do not be scared to try conicals without wads at all. In some cases you get excellent accuracy that way, as well.