Back in October 2015, Gmail and Google Inbox did not support universal links:
Note that Gmail and Google Inbox apps do not handle Universal Links properly (they will not open the apps). It’s not possible to open any app by any universal link in their apps.
Does Gmail and Google Inbox on iOS now support Universal Links?
The custom webview Google uses still appears to interfere with the Universal Links detection mechanism, so no, as of March 2016 Universal Links do not work with Gmail and Google Inbox.