I just drove up Skyline last week (Corona Entrance), but the gate was closed for the fire season. We were lucky enough to find the gate unlocked though, however other gates were locked up top. If you make it up, plan on going the whole way down to Ortega Highway just in case you have to.
Holy Jim road is only a few miles long and VERY rocky. The side trails don't really go to far and lead you back to the main road.