Just stumbled upon this question today:
"Is there a way to know that MPP published to the project server is not created using a template available on the server?"
Basically this comes from the point that how to find out compliance of the project plans to the standard templates.
I am not aware how it can be done?
Actually there is no way to identify by one field that this project was created using that template.
You may assume that by Enterprise Project Type, but again there is a way to change EPT for existing project.
The only way I know is to compare a template and a project by tasks, by structure, etc. it works like finger print recognition: you select several points which the most probably tell that the project was created from the template.
The worst case I can imagine: a user creates a project by a template and after that removes everything from the project. Formally the project was created by the template but in real there is nothing from the template left in the project.