The way I understand it flashbacks can come with hallucinations, though I myself haven't really experienced much of that...but I know some people do. I more just feel like the event is happening again and my hearing gets like way more sensative so I might like think I heard something I didn't hear and maybe sharper vision but no visual hallucinations.

So I guess I am not so sure it would be a hallucination or a flashback, more likely flashbacks causing the hallucination...so both. But its also possible to have other issues that could cause hallucinations aside from flashbacks so perhaps not all are.