I used to have a Volitan's lion. I kept him in a 125 gallon 'preditor tank' with a trigger, panther grouper, emperor snapper, snowflake moray, orbicularis batfish, and a queen angel. All got along fine.
The lion was able to be 'trained' to eat dead food by 1st putting it on the end of a broomstraw and shaking it in his face. Later, the same without the shaking, then I could drop it in the tank. From there it became easy to drop pellets or freeze-dried foods for variety.
Mine never was agressive to my hand but, I always kept an eye on him when doing maitenance.
Any fish 2/3 his size or smaller, crabs or shrimp are their natural prey and will be at risk. They will stalk or ambush them eventually.

On a side note about predator fish- I made a trip to Destin, Florida many years ago after a hurricane had blown a lot of Sargassum sea weed in and caught several, about 10-12 Sargassum fish. They all appeared to be the same size to me. I had the bright idea to add one to my preditor tank and bring the others to the local fish store for trades. I put them all in a large plastic bag inside a standard ice chest used for shipping live fish and flew home with my prize. When I got home I had only 1 Sargassum fish. The bigger fish ate the smaller fish until the largest one was the only one left. He died, of indigestion I guess, as he must have had all to-12 slightly smaller fish in his belly. It has made me never underestimate how big a fish a 'gulp' preditor can swallow.
So, moral of the story, if any fish is smaller than your lionfish, it may one day be fish food for the lion.

By the way. A lionfish sting is not usually fatal and is usually described as like a bee sting but the intensity may vary by species and how much venom was injected. The recommended treatment is soaking the injury in as hot of water as you can stand.