Changing out the tensioner pulley would not be a bad idea, especially while you're in there changing out the belt. However, it's not mandatory. Any of the pulleys up front are good until they aren't, but you can check it to see how it is fairing.
With the belt off, turn the tensioner pulley by hand.
- How does it feel?
- Is there any grinding or noise?
- How much wobble is there when you tip the pulley side to side?
If you get any noise or it feels like it's grinding when you turn it, replace it. If there's any more than a slight bit of tilting when you tip the pulley side to side, replace it. If it feels tight and is quiet as you turn it, it is most likely in good shape and you can leave it alone until the next time you replace your belt. You can also check any idler pulleys present in the same manner.