Actual documentaries would be OK. For Neda and Eyes on the Prize are great sources for the topics they cover. This is particularly true for events from the 20th century or later where a lot of primary sources are either audio or visual or both. There really isn't a better way to present such material other than in a documentary movie.
Of course the same caveats go with documentaries as go with written sources: they are created by living breathing human beings with their own beliefs and goals, and thus are never presenting a completely unbiased view of events. Some are less unbiased than others, and some even flat out lie. Same with written sources.
Biopics and other dramatizations on the other hand should never be used as sources. I've seen them used here where someone might mention a scene as a good way for a layman to get a feel for an event, but there always needs to be an actual source as well. I've also seen them used as the basis of questions about their veracity (and honestly we could probably do with more of those).
By their very nature dramatizations have to invent things, and there isn't always a good way to tell where the line is between presentation of fact and invention. This definitely includes Viceroy's House, which is a biopic.