Ps counts the mappings for the framebuffer as memory.
Especially on the FFB where a number of different mappings
of the device address space is used to optimize
access this can cause large amounts of memory, but not
physical memory, to be mapped and shown by ps.
It's not unusual for the FFB+ (Creator3D) to show a 500MB
process size for the X server.
Solaris 2.3 FCS also has a number of Xsun memory leaks when using
the SX. Get the SX patches or upgrade to a later release of
/usr/proc/bin/pmap (new in 2.5) will show the exact mappings used
by Xsun. "pmap -x" (new in 2.6) will even show how much of each
mapping is shared/private resident, etc. If Xsun has a memory leak,
you'll see a huge "[heap]" with pmap.