My recollection is that the dollar value discount codes aren't specific to any one person (which means in theory they could be transferable.)

Each discount code comes with its own terms and conditions --- if you have the discount code, you should be able to see the terms and conditions when you put it into your Mileage Plan account.

Companion fare discount codes and other promo discount codes are likely to have different requirements --- but I don't recall anything special for the dollar value ones.