Yes you can ono,

But depending on the strength of your preist (If they are normal 2 holy priests) they only have 2 options, Banishment or Blessing. And if there are no undead around they cast Blessing.

It may seem useless but it doesn't actually do much harm.

If you get more powerful priests and they are casting blessing when they are supposed to be casting Sermon of Courage howerver, this can be a problem.