Self Service is basically just a method for initiating the upgrade policy. You can have a policy do the same thing on another trigger. The question is the impact that would have on users who are now faced with an upgrade at an inconvenient time (they are either going to be impacted by it or cancel it if given the option).
I think that users would greatly prefer the ability to initiate the upgrade on their own. It's not something you want to force on an unwilling user.
@PLCH-Apple in the very brief testing I did with the VPP method I found that the app would only launch but would still require someone to do some clicking to get the upgrade going. You might be better off looking at a workflow similar to this. You could modify it so it wouldn't require Self Service at all. Or there are other methods such as a createOSXinstallPkg that you could use. What method you choose depends on whether you want user interaction or not.
If you're trying to get Sierra to your public labs, I used createOSXinstallPkg to get 10.11.x public macs to 10.12.3 via push and that worked. Then I used the Sierra Combo updater to get them to 10.12.6. It worked well for 10.11 macs, but not so well for 10.10 macs in my experiences here (+/- 400 macs).