Hi:
Louie sums its up to a TEE. If the lionfish can fit it into its mouth , its food.
I suspect the dwarf lion can eat the firefish no problem, however if the clowns outgrow the lion they might be fine
Marine fish usualy know what lion fish are all about and will keep their distance, but to play it safe when you do add the lion fish, do it in the evening and switch off your lights immediately after; the next morning everything should be fine specially if it is a dwarf lionfish. I always kept lion fish in my display lease tanks, tourists love them as they are very spectacular once big, used to feed them lean meat the size of my little finger only once a week till fully satisfied. PhilDor.