First of all, don't take "reef safe" at its face value. Reef safe usually means invertebrate safe (both sessil and mobile). Therefore, a lion can easily be kept in a full blown reef since the only invertebrates they normally eat are crabs and shrimp. So, don't plan on keeping any.
The second issue with lions is their fishy tank mates. Lions are not aggressive fish, they are peaceful and normally get along find with most other fish due to their poisonous spines. However, they will eat most fish that fit in their mouth. For this reason, many people keep lions with other large fish (these fish are usually aggressive).
However, as long as the other fish as too big to swallow (height can be very important when figuring this out), they can normally be kept with lions (unless they are too aggressive). Rabbit fish for example are good take mates.
If you want a larger selection of fish, a smaller dwarf lion might be the best choice. The fuzzy dwarf (which I have) preys mostly on crustaceons in the wild and does not get more than 6-7", making it much easier to keep with full grown non-aggressive fish. The dwarf lion gets a similar size and the fu manchu lion also (however, the fu manchu rarely takes to frozen food).
I would be more concerned about groupers than lions since they are more aggressive and less reef friendly.