Ehm.. yeah ok right.
So what would be the use of having your PHP scripts on a webserver that doesn't understand PHP?
And how can you use includes without using PHP?
And your include files would have to be stored outside the html document root, otherwise reading the code you could see which files are included, and simply request them.
Spiders are nothing more than automatic browsers. There is nothing a spider can do that a browser can't do.
So, if your webserver understands PHP, it will never show the sourcecode of your scripts. That's the whole point of PHP, to put sourcecode inside the page without it being shown.