Just to paraphrase the answers here more succinctly.
The answer is yes, php scripts in these pages will be parsed with no problem.
But, that is no guarantee that the variables/constants you are trying to use/manipulate with said php will actually be available/exist to use on that particular page. If you find that is the case, use the Superglobals plugin to find out what IS available on the page of interest.
Secondarily, you should edit these files with a plain text editor. Using a wysiwyg editor like CKeditor in a browser will mangle the php snippets when it saves the file. In CKeditor's case it turns them into html comments. There is info on the web about how you may hack it to prevent this behaviour. I spent five minutes not getting that to work: it was not worth the effort for me.
Steve
github.com/torvista: BackupMySQL, Structured Data, Multiple Copy-Move-Delete, Google reCaptcha, Image Checker, Spanish Language Pack and more...