I put a baby delhizi (~4") in with my 8" senegal. My senegal wasn't outwardly aggressive, but they stayed away from eachother. He got plenty of food when feeding time came around. The poor little bugger was scared to death all the time though, so he was always hidden in the plants. He lasted about 2 months, then one day he was dead. I don't know if he died in a fight or if the angelfish started picking at him after he died, but he looked pretty beat up.
A couple quick chomps from the senegal could have done it, but I wasn't there to see it, so I don't know. Anyhow, it is risky.
I say let the delhizi's be the star of their own tank as long as they fit. Let's face it: when a tank has a bichir in it, he is the focal point.