It depends on the dat. Some dats are more predatory than others, and prefer to eat bite sized tankmates.
I've kept dats with of various sizes when I had to, and with many other fish with no aggression whatsoever.
I had one IT a few years back that would eat everything that was bite sized. It tried to eat my freshwater stingrays tail one night out of the blue and that was the end of that. Apparently the tail looked delicious.
I've never had any other dat that was anywhere near as aggressive towards non-dats since then. I have 7 dats ranging from 3-6" now living with two 3-4" baby endlicheris and have had no aggression whatsoever.