Does the sentence use modifiers correctly?

We know that helium, commonly used in blimps and balloons, is actually less buoyant than hydrogen but safer to use because it doesn't burn or react with other chemicals.

Yes, the sentence uses modifiers correctly. The modifier "commonly used in blimps and balloons" provides additional information about helium, and the modifier "safer to use" provides information about the reason for using helium instead of hydrogen.