[Al Skierkiewicz]

Fox,
The point at which the chargers are sampling cell voltage, applying charge current and checking for load conditions are made at the processor level within each smart charger. There is no easy way to sync those cycles within multi chargers. Multiport chargers in the majority of cases, are simply multiple chargers within the same enclosure, with a common power line connection. I know that our six port charger that is available from many sources including McMaster is connected this way.
In my discussions with MK lab personnel and the Battery Council International here in Chicago, there are many "recommendations" made by manufacturers that are simply not good practice. In the case of simple chargers, where no switching/monitoring/status takes place, multiple outputs can be combined IF the chargers are connected to the same power-line phase and the total current does not exceed the max charge current specification.
Please note that the curves shown above also demonstrate the charge current during and after the addition/removal of an additional load in parallel with the battery charger.