There is the 'classic' structure of typical business dashboards as you have described, and the patterns that are common for screen scanning can be applied. However, I think the scanning pattern is also influenced by how you structure and present the content on the screen, so it is a catch-22 in some ways depending on if you are creating a new design or modifying an existing one.
I think to provide a more complete answer you will need to fill some gaps, but in general my advice on dashboard design would be to consider some of the following points:
- Blank, half-empty and full states: how will it look when the user sees it for the first time? What about when data is filling up, and also when the dashboard is completely full?
- Purpose: for dashboards designed for decision-making (i.e. Business Intelligence) you need to avoid cluttering and highlight key information, so this could definitely affect your design and layout compared to a typical reporting or status tracking dashboard.
- Widgets or visualization: depending on the number and type of 'widgets' used, there might be different alignment or layout strategies that are more appropriate than others.
- Viewpoint: depending on the actual size of the screen and devices that you are designing for, knowing that on most desktop setups in the office have dual monitors and the scanning pattern would be compared to single monitors.
There are probably other factors too but I haven't really experienced or look into it yet.
UPDATE (based on the screenshots provided)
You'd have to test this of course, but just thinking about the basic principles of good design (simple and clear) you would be creating additional lines of alignment and causing the user to move their gaze across the screen more with a centre aligned layout compared to a full screen one according to your design
Now I would necessarily say that citing the principles of design would be enough evidence to support your claims, but a quick test with some people and see how much quicker it is to locate and find contents on the page would probably do the trick.