If you place an alias of the Feedback Assistant in the, e.g., Applications folder in Finder, it will show in Launchpad, without having to pin it to the Dock.
In Finder, navigate to, or use: Go > Go to Folder…
Select the Feedback Assistant app and then drag and drop while pressing ⌥⌘ to the Applications folder to create an alias.
Feedback Assistant will now appear in Launchpad.
Note that while it will now appear on the last screen of Launchpad nonetheless, it can be dragged and dropped to where you'd like it on the screen or different screen.