Depends, most likely your aro is still small enough to view those type fish as a meal. Once your aro is bigger it may ignor the smaller tetras. I currently keep a school of black skirt tetras with my 4 arowana. When I tried giant danios they were devouered rather quickly.
When my larger black was 17-18" it would ignor cardinal tetras, but did eat the larger congo tetras that I put in the tank.
The silver dollars would be your best bet, if you get them big enough not to be eaten.