Hi Ian,
It is perhaps impossible to answer this one, some boards with on-board graphics may work OK whilst some will not. Mach itself needs a lot of the processors time and if the processors responds to an interrupt to service the graphics chip then the Mach timing may suffer and spoil the output pulse train.
Depending on the BIOS setup a PCI graphics card can often be used in preference to the on-board graphics chip which should then work OK (I have one such PC which works just fine but I have no idea of the board make and model).
Possibly the only way to be sure is to try it and see.
Tweakie.