I don't know if I'd bother with the rootone.
If there are plenty of roots left, and the crown isn't damaged, perhaps they'll survive. Knockout roses are pretty hard to kill. At least you're in the right time of the year to be doing this kind of work. Roses do well from drastic cutting back in the dormant season.
With such a damaged root system, watering will have to be carefully scheduled if you want them to live. Sprinker spray too much and you risk black spot (although Knockout is relatively fungus resistant), or crown rot. Roses REALLY like drip irrigation if that's an option.
But here's my thinking. IF the roses live, it will take a year for them to grow back to the 5 gallon size they were before. Will the customer be ok with waiting for that? And what if one or two die? Will they be ok with having roses of different sizes for a few years after you replace a couple and wait for them to grow in?
Last edited by rlitman; 02-24-2014 at 10:27 AM.