I just completed a run-thru of IWD1-HOW-TOTL and found my cleric to be enormously useful and capable at turning undead. By the time I was nearing the end of IWD1, he was blowing up undead with his turnings.
Just leave the cleric immediately behind my pally and fighter (while they're holding the line) and within a few seconds, most undead monsters within ... oh, say 8-10' will go boom.
I didn't really bother with turning in the Vale of Shadows. I didn't usually want the undead monsters running away. I wanted them to come to papa!!!