Yes DP is used for the "Third" of the three monitors for a proper Eyefinity setup. However, depending on what you believe, it is possible to use an active DP adapter to change DP into DVI. Now I've had nothing but bad luck with these in the past and I run a six monitor setup, two of which are DP monitors. I had no choice. I hear a lot of people got the active (read, ones that have a power supply of some kind.. USB or Wall Wart) DP adapters to work fine. You're mileage may vary.
- Urban Core.