There are natural "bugs" that break down oil also. So as long as the amounts are not more than what natural forces can handle, I would think it would not be a problem. Not like spilling a thousand gallons in one spot or something.
Many, many years ago, we used to use used crankcase oil mixed with kerosene to kill lice on our sow hogs. Dad would treat them a couple times a year as a prevention.
Oil seeps from the ocean floor all the time. Natural forces take care of it. The problems arise when nature is overwhelmed by excessive amounts.
In my non expert opinion.
