Dear Heidi, Many tour operators use helicopters to get people close to volcanoes.
Aerial views can be beautiful and give a good overview of a large area.
Since most volcanoes are stratovolcanoes the helicopters don't actually go down inside the volcano but do circle around the flank. I do know of a recent example of a helicopter that did go to far down inside a volcano. A crew from the U.S. mainland came to Hawaii to film scenes of the lava pond inside the Puu Oo crater for a movie. The pilot flew the helicopter through the gas plume above the crater which caused the engine to loose power. The helicopter crashed on the floor of the crater not far from the active lava lake.