If we are thinking of the same fish (most of the triggers in the Xanthicthys genus) they are generally fairly safe with corals but small fish and crustaceans are always a crapshoot. These triggers are primarliy planktivores in nature as evidenced by their upturned mouth structure. If you are adding them to a tank you would do well to add them last, after any smaller fish or crustaceans. Since you planned on keeping this with a lion I am guessing this is not going to be an issue. Also all triggers even the 'reef safe' ones can be nippy towards you the owner - they will quickly associate you with food and this can include your hand and fingers! They have a sharp bite so be warned.