Para windows, sim, para mac, talvez, para linux, não há menção a isso.
fonte Nas janelas
Video hardware acceleration support
Flash Player 10.3 supports hardware-accelerated decoding of H.264 video on Windows and Mac computers with supported hardware and drivers, providing enhanced video performance. For the latest information on supported hardware and drivers, visit the following vendor sites:
Intel hardware decoding of H.264 video in Flash Player 10.3 is supported on the Intel 4 Series chipset family and the 2010 Intel Core processor family with Intel HD Graphics, starting with graphics driver version 15.16.5.2021 (8.15.10.2021) for 32/64-bit Windows Vista and Windows 7.
For the Atom/GMA 500 chipset, hardware decoding is supported starting with graphics driver version 5.2.1.2020 (8.14.10.2020) for 32-bit Windows 7. Systems using GMA 500 video decoding should use a Windows Aero theme for optimal full-screen playback performance.
no OS X
Mac OS X hardware decoding support
On Mac computers, hardware decoding of H.264 video in Adobe Flash Player software is available with Mac OS X v10.6.4 and later on hardware supported by the Mac OS Video Decode Acceleration Framework (such as the NVIDIA GeForce 9400M, GeForce 320M, and GeForce GT 330M). Whether hardware decoding will engage for a specific video is determined by the Mac OS Video Decode Acceleration Framework. View hardware used by different Mac models