The Dual Link DVI adapter requires external power source as the DP source is not sufficient.
Yes, it is a real active adapter as it sources the power direct from the DP port.
Yes you can
AMD Eyefinity has been always linked to use the DP port. The only problem that this represents is that most users do not have DP displays and if you want to configure 3 displays, users have to use an active adapter of any source for their displays.
With the introduction of the new GCN architecture on the R7 and R9 series, AMD made this easier by using the two DVI and HDMI ports to configure 3 displays.
The only exception on the R7 and R9 series are the R7 260, 265 and R9 280 and 280X cannot support this feature as they still use the older architecture even though it has been classified as R7 and R9 Series.
AMD product advisory text on Tonga (aka R9 285) “Highlight for you in bold text”
AMD is pleased to share early information of a new performance ASIC variant, code name “Tonga”. The Tonga ASIC takes gaming to the next level, incorporating an improved and refined Graphics Core Next architecture, more advanced PowerTune power management, improved display connection flexibility, and enthusiast-level gaming performance.
In addition to the new architecture, the Tonga GPU supports the latest industry standards and is ready for Windows 8.1 with an architecture designed for DirectX 11.2, OpenGL 4.4 and OpenCL 1.2. The Tonga GPU fully supports resolution up to UltraHD (4Kx2K) over both DisplayPort and HDMI interfaces, supports up to six independent concurrent displays, and supports three of those displays to be driven from DVI/HDMI. Tonga will support Windows 8.1, Windows 8, and Windows 7.
The Tonga GPU is a PCI Express 3.0 compliant product. It supports a 16-lane PCI Express 3.0 bus interface for high-bandwidth applications. It is based on 28nm process technology, and is a RoHS compliant and Halogen Free ASIC.