I think, VBA in a Plugin is not possible.
But the access to all of the Mach3-Functions you have in VBA you have in the plugin too. The only thing it is in C, not VBA.
eg
in VBA:
Call SetOEMDRO (818, GetOEMDRO (818) * 1.1)
in C in aPlugin:
scripter.SetOEMDRO(818, scripter.GetOEMDRO (818) * 1.1);
VB should be possible, but not VBA I think.
In both cases you have to compile those scripts or you have to build your own interpreter.
That's all, not more, not less.
Bye, Steffen