Left untreated, oil spots on asphalt can slowly eat away at the binders and can cause irreparable damage. With that in mind, it might be better to clean them yourself rather than waiting for the next time you hire a contractor to reseal your driveway to clean them.
Clean oil spots using a commercial de-greaser, a broom and water. You may have to brush and rinse a few times to get all of the oil off but in the end it's well worth the effort. Just be sure to completely rinse off the commercial de-greaser entirely.
See our report on “The Most Common Ways Asphalt Repair, Maintenance and Sealcoating Contractors Rip Us Off and How To Avoid Them" and avoid the pitfalls of hiring the wrong contractor!