The Marvel Omnibus releases, together, are collecting all of (or at least, most of) the previously released Dark Horse content. In order to collect everything, you're going to need the currently released Vol. 1, the upcoming Vol. 2, and any future numbered Volumes that follow (Vol. 3 is already announced, and presumably we should be getting at least a Vol. 4 as well in order to reach the end of Dark Horse's output).
There is no overlap between the content included in Vol. 1 and Vol. 2.