Yes, take him. Then we have four good guards, which is slightly crowded but not too bad, especially if Smart spends some time at the 3. I think Dunn fits next to any of our other guards, so it's not a problem in that respect either.
Basically, it's rare that you don't draft BPA at that spot in the draft. The only time that you don't is when it's really close in terms of talent and there's a big difference in terms of fit. Neither is the case here.