if you're not sure about how the printer will manage it, you should flatten the transparencies (or avoid using transparencies).
printing from acrobat reader to .ps and converting the .ps back to .pdf will take care of flattening the transparencies.
from my recent experiences, ghostscript seems also to be able to do it! you may want to try the round-trip conversion with it, if you prefer to work with free software.
... sadly, scribus can't do it on its own (it's an hard task to do it correctly) and printers don't always fully support pdf versions which contain transparencies (1.4 upwards)
hope that helps
a.l.e