Chopped or whole?
You don't have to toast them first, but if you do, the oils will brown a bit and taste toastier. So, yes, I'd toast them, just to add another dimension of flavor to the brownies.
Chopped and lightly toasted. Yes, please.
By all means toast them. 350 degrees until fragrant, then roughly chop with a knife. Toasting them not only adds another layer of flavor to your brownies, but it also gives them a pleasant texture, unlike the "pencil eraser" texture of untoasted nuts.
Chop then toast in 300 degree oven for 6-8 minutes or just until you can smell them. Totally enhances flavor and texture!! So worth the extra step!
If you sprinkle chopped nuts on top of the batter, they will toast perfectly during baking time and it saves you a step! Plus picky eaters can easily scrape them off :)