No, you get the enzymes for conversion when the grain is sprouted and malted. The roast barley isn't sprouted, but more importantly it's pretty much charred. The oats will add starch, protein, etc. to contribute to mouthfeel and sweetness, but in this case it's going to be hazy beer from all the excess starch.
Adding a little base malt will do the trick. One pound of pilsner or 6-row will have plenty of diastatic power to handle a pound of oats. If it's further diluted with the roast barley, perhaps go to 2 lbs of pilsner/6-row.
Originally Posted by ericbw
Will the starch in the oats convert with only roasted barley and no base malts?