Sim, você precisará usar o DisplayPort para acionar um terceiro monitor.
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Thanks to some firmware and board level changes, with the 200 series AMD is now able to attach multiple TMDS transmitters/interfaces to the same clock generator, allowing one clock generator to be used to drive multiple displays. As a result it’s now possible to drive up to 3 TMDS interface displays off of a single 200 series card, albeit with restrictions.
The catch here is that these can’t be independent displays, and this change is primarily intended towards enabling Eyefinity with cheap, DVI/HDMI-only monitors. To utilize clock sharing and to drive 3 such monitors off of a single card, all 3 monitors must be timing-identical, which functionally speaking almost always requires the monitors to be completely identical. Furthermore the sharing of the clock generator can only be engaged/disabled upon boot, so the 3rd display cannot be hot-plugged and must be present at boot time. Consequently this is by no means as unrestricted and easy as having native support for 3 TMDS interface displays, but for Eyefinity it will get the job done.
Of course this restriction only applies to using 3 TMDS interface monitors off of a single card natively. Using the DisplayPort, either with a native monitor or through an active DP-to-DVI/HDMI adapter, still allows the same fully independent functionality as before.