Generally speaking, you use a tab bar controller to move from one "root" view to another within the flow of an app. A toolbar on the other hand is used to execute various functionality within a given view. So, it kind of depends on if you are using this as a tab view controller or a toolbar.
For an example (same as the HIG), look at the clock app, which uses a tab bar controller to switch from one root view to the next. And each type of clock has a unique flow.
Examples of toolbars are pretty extensive across all the native iOS apps.
Given the established UX from the native iOS apps, controllers, and the HIG, if you present your events in a modal fashion instead of pushing them onto the navigation controller stack - you could probably get away with "multiple" tab bar setups. I've never seen a tab bar change as a result of a view being pushed onto a navigation controller stack - I have seen the tab bar disappear and be replaced by a different UI component altogether (see the Music app for an example, the list views have a tab bar controller - while the "now playing" has play/pause/volume).
But, honestly, I may not be fully understanding the question or desired outcome. This is what I was able to infer from the wireframes and phrasing.