The Late 2012 mid-range Mini (2.3 i7) ships with 4Gb RAM and the Intel HD 4000 chipset, and allocates 256Mb to graphics I believe.
I have just upgraded the RAM to 16Gb (thanks OWC) and the System Report shows that currently 768Mb is allocated to graphics.
So adding physical VRAM, no; the machine allocating more RAM to graphics, yes, by adding system RAM.
Hope this helps. Will add an SSD to the second slot in the next week or so and the little mini should be purring along nicely.
Ben