Hi Alan:
Sure you can.
You can wire EDM both copper and graphite...copper is much easier to wire than graphite, and makes very nice electrodes for the sinker.
Using a sinker to make "reverse" electrodes is possible too...graphite can burn into copper very easily, and copper can burn into copper.
I've never tried burning copper into graphite though.
You have to ask yourself though...if you're able to mill the first electrode, that's going to make the second electrode, that's going to burn your final shape...can't you just simply mill the final shape into the job??
I've hard milled up to 60 RC with coated carbide with no major problems.
Milling is much faster than EDM and has better dimensional control too.
I realize that there are circumstances where it's still a better choice to burn the shape even when it could be milled, but I thought I'd throw this comment out anyway, just in case it didn't register when you planned the job.
By the way, how are you making out with your Hansvedt?
Cheers
Marcus