Is onboard graphics card using virtual memory

It is using a part of the system memory. User specified amount.

^^^

And system RAM is generally slower than Video RAM (VRAM).

It depends on the onboard GPU. Some HD3300s and HD4200s from ATI in the 790GX and 785G chipsets have dedicated memory called side port memory, this allows it much faster access than system ram, however they also share system memory to allow them to handle heavier tasks than their 128MB of sideport memory allows.

Virtual memory is images of the memory, pages, that are saved as page files on your hard drive, this allows your system to behave as though it has more ram than it does, however accessing these page files is incredibly slow relative to regular memory.

No matter what onboard graphics you have, it definitely isnt making use of virtual memory.