For windows, yes, for mac, maybe, for linux, there's no mention of it.
source
On windows
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.
on 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
