a "vertical integrated stack" is something like this: On the bottom you have hardware designed, made and maintained by vendor X. Based on that, there is an operating system developed, integrated and maintained into said hardware by vendor X. On top of that, there is a database, developed, integrated, maintained by vendor X. On top of that the same story with the application server. On top of that... the ERP system from vendor X.
These "stacks" have the advantage that system integration/problem rectificiation costs are typically much lower than a "best of breed" approach were you take the hw, os, database, app server and ERP from a different vendor each.
On the other hand, vertical integration breeds tons of inefficiency, bureaucracy, huge headcount and excessive cost. Look at IBM in the early 1990s and you will understand.
Oracle was highly successful with a different approach: Selling the Oracle RDBMS for all conceivable hardware/operating system platforms. From VMS to NCR via Unix, so to speak. They ate lots of business from IBM, who were vertically integrated then (they even made their own RAM and harddisks).
Now Oracle acquired SUN and they need to spin this. So they praise the "vertical blabla". We will see how this "pans out". I am highly sceptic. Intel already killed SUN and the Oracle hw biz ist next on the list.