Yes, reef sharks have the potential to become a serious issue for a lion fish hunter - see DAN's Alert Diver article,
A Shark Tale. From the article:
"Art had just speared two lionfish and was heading back to the boat when he attracted the attention of a couple of 3- to 5-foot-long Caribbean reef sharks. They were drawn by the fish blood and dying movements of the fish on the end of the spear. One shark swam up under Art as he made his way toward the boat. As the shark opened its mouth and headed toward the fish, he encountered Art’s left hand instead. Art says it was sudden, unexpected and painful. He tucked his fist under his right armpit and continued to the boat, where he handed up his fish. Sue and Paula then helped him aboard, applied a pressure dressing and helped him remove his suit. There was a lot of blood. Art doesn’t remember any of this."
So far I have never attempted to spear lion fish. If I did consider it, I'd want to know about the likelihood of encountering sharks in the region I planned to do it, and what species were most likely to be seen.