Some of them are professional, some semi-professional, and some of the people in a few of the pictures are tourists. The guys getting close to take the pictures are professionals.
Having been to the lava flows in Hawaii, it was scary (and extremely hot) enough just to be 50ft. from a glowing red crack in the hardened surface and not know how thick (or thin) the crust was we were standing on. We, and many many other tourists, had ventured past the recommended "safe" zones. As a tourist I would never get that close to an active flow - way too hot and unpredictable.