I dont think any arowana can be considered docile when another arowana is involved- but both SA aros seem a bit more tolerant than asians and aussies-
something else that Ive noticed when mixing arowanas, is not to worry too much about the lengths of the fish- the height is much more important for an even match- so if a black arowana is 18" long and 3" tall, an asian might only be 12" at 3" tall- and the same applies to aussies also-