I would definitely make sure you either beef up those dats for a while or buy a good sized dat before you add an aro. Like T1KARMANN said, the growth rate on an aro is MUCH faster than a dat.
In one of my tanks I have dats mixed with Ctenopoma acutirostre (See my Avatar), and L. desmotes, and there is no aggression towards any of the tankmates. Their is occasional chasing between the other ITs, but nothing major.
In two of my other tanks I have aros and dats. I have some with a Jardini and some with a Silver and I haven't had many issues. The only thing that happend was one of my ATs nipped up my silver, but nothing bad. Other than that they have been one happy family.
One other note...I've actually had great luck with clown loaches and aros enticing my dats to eat pellet and other prepared foods, so you may have luck with switching foods buy keeping active feeders in with them.