Can bleeding be caused from diverticulosis or diverticulitis, or either?

Either: These two are essentially the same diagnosis - small outpouchings if the wall of the colon. "itis" is inflamed, and can cause blood in the still, but not quite like "osis" bleeding that can be severe.

"-osis" bleeds.: Our general medical tenet is "diverticulitis doesn't bleed." Diverticulosis can bleed, and the bleeding is rather brisk and scary but tends to stop on its own after a while, not that it shouldn't prompt a visit to the Emergency Room to be safe.