LEL monitors are typically area sensor/alarms that calibrated for a specific gas - methane, propane, whatever is likely to be the fuel. I believe that there are catylytic bead sensors in LEL that are somewhat generic, but most of what I see are specific monitors for gas in the area.

Oxygen sensors (in the same sentence) are most likely used to alarm when the oxygen in the atmosphere is depleting or being displaced by some other gas, endangering human life.

However, there are oxygen sensors used in process measurement (waste water biological activity, boiler water corrosion potential, fish breeding health,etc) that have little if anything to do with LEL, so the answer to is it enough, is, it depends. Both on-the-job fires and deaths usually incur liability.