Are those a notho variety? In theory it can work, the potential issues i can see are 1. make sure the killis will be ok in your water. Some annual killis like it a bit cooler than your dg. That is probably workable though since most fish are pretty temperature flexible. 2. be cautious because some killis are rather aggressive feeders and can be nippy. Dg seem to move rather slow, so be watchful of their interaction.
A trio of those should be fine in a 30g though, just make sure to research the species a bit for it's specifics to see if it's compatible with your other fish.