Yes you can, just cut them up not too small they shouldn't take more than about 40 monutes although can can cook them longer, I just put mine in with the chicken raw spray a little bit of sunflower oil on them, although you could par boil them if you wanted to. I love sweet potoatoes when roasted.
They also microwave really well. Prick a few times with a fork, then micorave on a plate with a piece of kitchen paper over it. About 8 minutes initially and then for a few minutes at a time until soft. The skin should then peel off easily and the innards can be mashed with a fork (or put into a soup)