Hi mate,
I think where that post goes wrong is that the URL is case-sensitive.
In particular it is important to always use "dashboardId" (case sensitive) otherwise if you use "DashboardID" it will always default to your default dashboard, ignoring whatever GUID you have provided.
In my use of linking to Dashboard URL's with CRM Online there is definitely two ways (with slightly different results), both useful depending on your requirements.
1. Without Dashboard Title / Dashboard Selector
https://yourcrmorg.crm0.dynamics.com/dashboards/dashboard.aspx?dashboardId={GUID}&dashboardType=1030&pagemode=iframe
** dashboardType= 1030 is for System Dashboards, 1031 is for Personal Dashboards
2. With Dashboard Title /Dashboard Selector
https://yourcrmorg.crm0.dynamics.com/workplace/home_dashboards.aspx?dashboardId={GUID}
Hope that helps.
P.S. I used some of these techniques as part of a solution called D365 Tiles that allows users to create a nice Windows-style TILE interface for dashboards or forms. It will be live shortly on Microsoft AppSource, but in the meantime check it out: http://miiia.com.au/add-ons
Cheers,
Dan