According to a post from Klaus Staedtler on comp.os.os2.multimedia the recently released new 2.58.144 driver was briefly listed on Matrox's site
as supporting the G550, but was changed back to G550 "not planned" under OS/2.
http://www.matrox.com/mga/support/drivers/unified/home.cfm
ftp://ftp.matrox.com/pub/mga/archive/os2/2002/os2_258.zip
Source: OS2VOICE