Omnifocus or Drafts tags?
If Drafts, you can set that in the Action settings - After Success, Assign Tags.
If Omnifocus, the action should be pasting in Taskpaper format ou just appending an @tags entry should suffice.
But I’ve just tried it and it isn’t getting interpreted as I had expected.
But it looks like it should work based on these:
https://support.omnigroup.com/omnifocus-taskpaper-reference/
It’s late for me and I’ve probably just overlooked something that someone else will spot in 2 minutes.
But for what it’s worth, here’s an action taking both aspects.