The NPS map http://www.nps.gov/common/commonspot...&parkname=Zion shows that road as being paved until just before the reservoir. I drove up there once, stopping at the end of the paved section because I had a rental car. There are some trailheads on the road for backcountry hikers.
IMHO if you've only got a limited amount of time then it would be better spent in Zion Canyon, where the shuttle bus goes - but that's just my opinion.