If you had a Citi credit card that was included in the Citi Thank You Network you would be able to get credit in your Thank You account for every mile flown by anyone for whom you buy a ticket. The Thank You account miles can be used for flights on any airline. There are some FTers who LOVE this program and there are others who feel the unusual redemption rules are less flexible and/or worthwhile than some other credit card programs. With this program you would not be able to have the Thank You points put directly into your DL account but you would be able to use the points to get tickets on DL or any other airline depending on what airlines are available for a particular itinerary you desire. By the way, you would also get the frequent flyer miles with any airline for the miles flown on an itinerary using Thank You points, unlike the usual award ticket rules whereby you get no FF miles. You can read more about the pros and cons of the Thank You Network in the "other credit card" forum.

The only airline frequent flyer program I know where you can have access to miles earned by another person is BA, where spouses can have a family account. Each spouse's miles are tracked in individual accounts with different FF numbers but you are also shown on the BA site the total miles earned by the two of you together and either spouse can draw on this collective amount for an award. A very useful dimension that I wish more airlines would adopt.