Third party PCI Video Cards can support sleep. Card developers are responsible for supporting the sleep features provided by the Power Manager.
In Apple's "Designing PCI cards and Drivers for Power Macintosh Computers" document, Apple sets guidelines for power management for specific classes of drivers. To be compatible with the Energy Saver control panel, graphics drivers should support the GetSync and SetSync status and control calls to implement the VESA Device Power Management Standard (DPMS) for power management. This allows the Display Manager to handle all interaction with the Power Manager on behalf of the driver.
Support Information Services