Keynote, hiding objects during printing
Guides are the only non-printing elements in Keynote.

You can either use a duplicated set of masters (e.g. one master which includes your guide elements and one which doesn't). Then either manually switch masters before printing or delete the guide-elements master and replace with the non-guide-elements master.

Or you can insert "regular" guides (drag out from the rulers) on your master slides, then enable "View Master Guides" (Keynote View menu > Guides > View Master Guides) to show the guides from the Master slides on the "regular" slides.