There are a couple of misconceptions here that should be cleared up. Own-root roses really have nothing to do with Knock Out roses, although it's true that Knock Out roses do grow well on their own roots. An own-root rose is any rose that's grown on its own roots instead of being grafted. Keith's seedlings are own-root roses.
Grafting doesn't make plants hardier or more disease/pest-resistant. The rootstock might be hardier or more resistant, but the rose itself will retain its innate qualities. This is the reason that the Dr. Huey rootstock is more likely to take over in colder zones. It can be hardier than the rose that's been grafted onto it. Grafting can and does add vigor to most roses, and this is the reason that so many roses were always grafted until recently. Many hybrid teas, for instance, will not grow well on their own roots because they aren't vigorous enough to grow large and to produce many blooms.
