I must say, reading on this page, that if this SDK would do the same for all setups, it would be godsend for multi-mon support. On the other hand, if using this SDK makes developers lazy, so they won't implement support in other ways for multi-mon users (TH2G, Nvidia surround), it works like a vendor block even if not intentionally.
Your post got me curious, Tamlin, so I went on an information hunt regarding the SDK.
Compatibility information is plentiful:
http://sites.amd.com/us/underground/products/eyefinity/Pages/eyefinity-sdk.aspx
http://developer.amd.com/gpu/ADLSDK/Pages/default.aspx
From the SDK documentation:
Regarding Eyefinity, the SDK documentation has detailed information about how the ADL works:
Here is a snippet of the code itself, showing how the system is queried for an EF display configuration. Take note of the next-to-last line containing the "Eyefinity configuration query failed" message:
And the result of running the sample binary from the SDK on my system (NVIDIA+TH):
This should not really be surprising, but when it comes to multi-mon support ATI's purpose (as openly stated) is to make it as easy as possible for developers to support Eyefinity on Radeon 5xxx GPUs. Their tech won't naturally integrate with competing products and it would be silly to think they would go out of their way to help NVIDIA or Matrox. Such is the nature of business.
As is seen by the recent discovery regarding Splinter Cell: Conviction, developer support for Eyefinity may mean nothing for Tripleheaders. If Ubisoft enabled EF by utilizing ATI's SDK, then they will have to implement a different solution to get Triplehead to work (and yet another for NVIDIA Surround). If this becomes the standard practice by developers going forward, then what we have is an industry cluttered with vendor specific/exclusive multi-monitor solutions. Such a fragmented market doesn't bode well for us gamers. :(
PS-I fully expect Ubisoft to take the lazy road, whatever that may be.