Can you send me an example of something that's not showing up?  Chromium Dash polls Gitiles, not Gerrit, so I don't think the code review tool used should have any impact here.  It's possible that the commit message is different though, and as a result it's not parseable - but that's something we can fix.

So, since I moved to Gerrit on Chromium none of my changes are showing. For example, the last two ones here:
https://chromium-review.googlesource.com/q/owner:fserb%2540chromium.org+AND+is:merged
like:
https://chromium-review.googlesource.com/c/517965/
and
https://chromium-review.googlesource.com/c/518262/

are not showing up on my dashboard.

CC'ing agable@ as the best POC for PolyGerrit implementation I know of, but please re-route if need be.  I believe this is a PolyGerrit issue.

They're not showing up on your dashboard because you log into Chromium Dash using your @chromium.org account, but commits landed with PolyGerrit appear to be attributing your @google.com account as the author.

For example, for https://chromium-review.googlesource.com/c/517965/ (which lists owner as fserb@chromium.org) Gitiles has the author listed as fserb@google.com, see https://chromium.googlesource.com/chromium/src.git/+/1497017e0dcacd563f483323550e77d32f536d87.

agable@, is that WAI?

fserb: please run "git config user.email fserb@chromium.org" in your chromium checkout. (Or set it globally in your ~/.gitconfig file.)

arghghhhh. :)
Done. 
But why does it show the right email on PolyGerrit but not on the commit?

Because your accounts are linked (see the section about linked accounts on polygerrit.appspot.com). If you go into Settings, you can pick one address to be your "primary", and that address is shown in all places in the UI.