Can diverticulitis and diverticulitis cause complications with crohn's disease?

Not really: You can have both diseases, with each having potential to cause serious problems on their own. The two do not aggravate each other in any direct way.

Maybe: It is possible for underlying ibd to complicate post-operative care of patients requiring segmental colectomy for complicated diverticular disease (i.e. Perforation) especially when it comes to reversal in the setting of active ibd.