As has been said 89 is a good paved road with no issues.
If you are at Kodachrome SP as long as you go north to HWY 12 then west to 89 no problem at all. If you are thinking about going south out of Kodachrome SP down to 89 then yes that is a dirt road with a fair amount of washboard. It is a long haul on a slow road with a lot of washboard and a couple of really good steep grades. Part of that road is very pretty the second half or so not so much. I have taken a popup trailer up that road from 89 up towards the State park and made it fine but it was not the smartest thing I ever did. No way would I take a motorhome, travel trailer or fifth wheel. A class B would probably be ok However since you are going to Virgin there would be no good reason to go that way since it will take longer than the highway.