Yes primary radar can see glass ships. The metal push rods provide a
visible return. I once enjoyed having Tucson approach vector airliners
round me while I climbed on the edge of their class C airspace. That
was in an ASW 19. The radar can be set to reject slow primary targets
so they may not see you if they are not looking for you.

Being a possible primary target won't give you much protection though
unless you are talking to ATC. At best conflicting traffic will get a
report of "traffic 12 o'clock slow moving altitude unknown". You will
be invisible to TCAS.