Hi Eric,
I believe you can't directly add a User to the People Tab. However, as soon as you add a User to an Assignment for a Task, that User is added to the People Tab (I'm sure you are already aware of this. :-)). The good news is, you can remove the User from the Task Assignment and that User will still be in the People Tab (For some people, this is not a good thing.) This way you don't preload the User to a Task for all Projects convert with the template.
If your goal for adding Users to a template is to inform on Projects created from said template, I might suggestion adding those Users to Project Sharing for that Template.
I hope this helps.
Joaquin