Yes it will with the InterLink. If you have both units setup to fully participate in the network; than marking a waypoint will save the waypoint to the unit you marked it on, it will save it to the InterLink and save it in the second unit as well.

With those two units though you could Ethernet connect them. Saving a waypoint on one unit will make it available for use on the second unit – but without taking up any memory space on the second unit. There are also other sharing possibilities with the Ethernet that the InterLink cannot be made to do.