It might work that way - try it! But it strikes me that you will simply be doing what Acrobat is doing, only offline instead. It depends what the plotter driver generates. But this could be handy if you're printing the same drawing more than once.
I am not sure whether PDFs can efficiently handle line drawings so that they can be converted efficiently to HPGL. I suspect they can, as I have tried printing out a manual that included line drawings on the same laser printer using both its PCL driver and its Postscript driver. The printer's Postscript software did a much better job of the drawings than my computer.
Sadly, I don't think there are any Postscript cartridges for your plotter as that would be an ideal solution.
FYI:
PDFs are like Postscript documents in a wrapper
http://en.wikipedia.org/wiki/Pdf
HPGL is a list of commands like: pen up; pen down; gotoXY.
http://en.wikipedia.org/wiki/HPGL