If I follow the link* in the CDash update info page (e.g. https://cdash.mitk.org/viewUpdate.php?buildid=7415), it does not work.
*: https://phabricator.mitk.org/diffusion/DIPP/commit/ae21cdc4462755e340d86f0e488c6c44c4970058
Selfe generated links like https://phabricator.mitk.org/rMITKae21cdc4462755e340d86f0e488c6c44c4970058 do work though.
It might be that CDash gets confused due to MITK extension features and tries to find the commit in the wrong repo (DIPP instead of MITK).
The quick fix would be to change the repository base URL in the CDash project settings to MITK but I guess the preferred solution may be something like a setting in the MITK CDash script to decide if MITK should be the repository of interest or an MITK extension should be the repository of interest. Thinking about it, it probably must be a combination of CDash project settings and CDash script as we cannot change project settings from script but probably we can somehow achieve to report a revision from another repository than MITK in the update step.
I looked into the CDash script and to basically "swap" the primary repository would induce many many new lines of code. Hence, I vote for "let's always keep MITK as primary repository that reports its revision but change the CDash settings to the MITK repository instead of the MITK extension's repository". Tl;dr: Make the revision links work in the web UI but they will always link to MITK, not an MITK extension.
Oh, I just noticed an "Add repository" button in CDash. There may be the possibility to actually report revisions of more than one repository. Let me check that... :-)
As the devs of CDash prefer to stay dead silent about this feature both in the issue linked above and on the mailing list, I think we can make an educated guess that it is not implemented.