Do all viruses incorporate themselves into the host cell's genome? Or is it just retroviruses? Can any DNA viruses do this?

Also, must a virus be capable of incorporating themselves into the host cell genome in order to be oncogenic? Or are other oncogenic mechanisms possible?

Thanks!

Good questions!

No the majority of viruses just hijack the synthetic machinery of the infected cell to produce more viral particles that usually kill the cell liberating the virus which in turn infects other cells and in time other organisms. That does not usually involve incorporating themselves into the host genome. Some viruses do that and as you say are called retroviruses.

There are multiple mechanisms by which DNA or RNA viruses cause cancer (oncoviruses) which again is not necessarily synonymous with genome integration - see below
http://en.wikipedia.org/wiki/Oncovirus#History