if you plan on locking the dog up in this area, then it would be a bad idea. Locked in a room with carpet, a dog will tear it up and do their business on it. Otherwise, it is not an issue. Accidents will happen if it is a puppy, but it is easily cleaned up.
In all my years of training and keeping dogs I have only had one that could not be kept in a house with carpet. This dogs loves carpet and does her business on it. She is completely house broken, but if there is carpet she just HAS to go on it!
I say if you want carpet go for it! The dog wouldn't matter.
Cons would be: Wet dog, if it is raining pup will come in and rub all over it to get dry. Wet dog smell.
If it is a large dog, the carpet will smell like dog. If it is a small dog, this is less likely.