Nope, no need to parboil, only takes 20-30min. I've just had exactly that for my tea! And it was diviiiiiine mmmm, sweet potatoes cut into wedges, sprinkled with Maldon sea salt and Cajun seasoning, bunged it in for 20-30min *drool* Had it with boiled egg, salad, jalapeno hummus and raw veggies to dip in. om-nom-iferous!
I never even par-boil "normal" potato wedges. Just chop them, spray with frylight and sprinkle with seasoning and then chuck them in the oven (on high) for about 30 minutes, turning half way through.