Its not unusual to hear "no slugs" in reference to full choke. But measurements and metallurgy will allow it. Common Foster slugs rattle down the bore of most 12 ga's anyhow. They will clatter through the choke and go their merry way.
Not recommended for accuracy, but in most cases, possible and safe. Only thing I can think of is if somebody pressed/sleeved a choke tube in the gun that is absurdly tight. But a factory, fixed, full choke will handle a slug, though likely not w/ best accuracy.