Would the alert point to many different dashboards, depending on the output? If they all point back to the same dashboard you can just use the dashboard link in plain text. Slack should auto format it as a link. The link will be something like https://splunk.mydomain.com/en-US/app/search/myDashboard
If you need different dashboards for different alert outcomes, you are probably going to need multiple alerts.
Thanks for the response Richard. Each alert would point to the same dashboard but with different token inputs. I'll give it a shot.
I just tested this with some form.field inputs and slack did format the link. I was able to click on it, and get the populated dashboard.
You can, of course, also do form.field1=$result.foo$ to populate the dashboard with results from the search.
Alternatively, if it's different dashboards based on the results of the search then you could use sendresults https://splunkbase.splunk.com/app/1794/ (or it may make more sense to have multiple alerts).