First, Intel Celeron/ Pentium based on the Ivy Bridge micro- architecture has an Intel HD Graphics not HD2500.
Second, the differences between these two GPUs are quite insignificant.
Graphics support for HD2500 comes on 10.8.3 and above.
Without core graphics implementation like 10.7.5/ 10.8- 10.8.2 you are able to make a regular boot of your OS X, because no kexts are loaded. Of course, no QE/CI is enabled.
Chimera /IGPEnabler/ and Chameleon /GraphicsEnabler/ gave me the same result when trying to enable HD Graphics on 10.8.3 and above- half colored screen with lots of artifacts. Absolutely the same as HD2500.
G1610 is a very impressive middle- class processor and if in the nearest future its GPU starts working it would be very nice.