I use VISO as a power supply for OUT signals pull-up as shown below.
Is it OK to connect two ADuM6400 VISOs together?
There is no issue connecting VISOs together, however the device with the higher output voltage will provide all (most) of the load current. In other words, the two parts will not share the load current equally, as the load demand increases the parts will tend to share more equally.
There are other parts in the is product family which do support load sharing, such as the ADuM5401 which has an RCout pin which can be connected to the RCin pin of an ADuM5202. Depending on the voltage isolation required, I can assist in finding parts that can help with your schematic.