If you have an older gas oven or stove that uses a standing pilot light then yes you should be able to use the gas oven with the standing pilot light during a power outage.
However most new gas ovens today use an electronic ignition that heats up and then lights the gas burner on the oven and in that case you won't be able to use the gas oven when the power is out even though you'll still have gas service to your home.
You can still light the burners on the gas stove though for the cook top with a match or lighter even if it's electronic ignition.
If your gas oven was made in 1990 or new than 1990 then it's electronic ignition and the oven cannot be lit without power being supplied.
You could hook a small generator to the oven and run an extension cord outside to supply power to the oven to light it that way as the oven igniter uses very little power for ignition and to open the gas valve.