"I have a link stating Windows Server 2012 should work"
Which is why I brought up the 2850 ... the OS may be supported by the Dell on a given machine, but some features may not be, and I believe it is up to the user to determine if the system will support the planned needs of the upgrade. The only other option is to not support 2008 or 2008 R2 on a 2850, which would be an extreme position to take, leaving many people with decent hardware out in the dark to muddle through with an ancient OS, given the fact that the hardware will otherwise run the OS wonderfully. Likewise, Dell supports 2008 (non-R2) on a 2650 too, but since the 2650 is 32-bit only, other limitations are in effect as well.
So, while I don't think that blanket statements/requests should be made - that it is all or nothing - I do believe adequate documentation on the limitations should be made available. A "supported features" document would be great.
However, there is still little to explain why Hyper-V 2012 will not work on a 2950. The only published requirements for it are:
1) VT (all 2900 processors support VT-x, not all support VT-d, which should not be a deal-breaker), and
2) XD must be available/enabled (all 2900 processors support this but should be enabled in the BIOS, which from my understanding, without this setting in place, the OS will not even install).