Kind of. You can enable 'developer mode' on a consumer Xbox One which allows you to run unsigned apps (UWP) but it doesn't give you full access like you would get with the full SDK which gives you a load more diagnostic, debugging and telemetry options.
It doesn't allow it to run a ripped game like Halo 5. Any "real" game that needs full access to the Xbox hardware needs to be signed or tested on a proper dev unit. The 'dev mode on consumer consoles' is something for indies and such to test their UWP apps on. If someone happens to have the source code and project files to your UWP app then sure they could "pirate" it but I am not aware of that ever happening.
