While each fish is an individual I have kept a niger with all 3 of the volitans I've had over 30 years without incident. Tank needs to be at 180g, smaller tanks will present more of issue with aggression as well as both will reach about 12".
If the tank is big enough it could work. Also rock work is important as lions tend to like to hang out in caves and over hangs and triggers need rocks that they can wedge into at night to feel safe. I think many times comfortable surroundings are not provided for fish in our aquariums and can contribute to aggression. This is just my observation and not based on fact.
Nipping is always a possibility with triggers. I had a Niger that was fine with any fish. I did have a volitan but only for several months and the Niger didn't bother the lion. Unfortunately the lion stopped eating and passed. Tank was a 180 gallon.
If you do try it I would recommend having a backup plan in case you have to remove the trigger.
I had my Niger for over 6 years and it was about 7 inches tip to tip when it started munching on my LPS so I rehomed it.