Diverticulosis is exceedingly common. According to numerous reports I've read on the subject, it would seem as if there are indeed very few colons out there that are completely free of any form of diverticulosis. Straining when constipated is a large contributory factor in diverticula "popping" out as bulges in the gut, especially the lower colon. Hence my own logical deduction that, if anything, enemas should contribute to the prevention or hampering the progress of diverticulosis.
Obviously, diverticulosis will be worse in some cases than others, and when the diverticula become inflamed (diverticulitis) it can be anything from uncomfortable to painful for the sufferer. The question is, however, if taking enemas while having diverticulosis is dangerous. And here we have to admit that we don't know. For people with a predisposition to gut perforation, putting ANYTHING into the colon may be dangerous. But then, this type of predisposition is not common at all - in fact, it is very rare. So I would think that for the majority of people, diverticulosis or not, enemas won't be dangerous at all.
My own feeling is that regular enemas actually strengthen the gut muscles and tissue, and that it may even be the solution to prevent conditions such as gut perforation, when done sensibly. And sensibly means listening to your body and pain thresholds, and looking out for signs of trouble, like bleeding, etc.