Well... Based on the way you chose to phrase your question, yes. Keep in mind that the web server (whatever is "cooking" your HTML) needs to explicitly execute the stored procedure, that processs doesn't happen "automagically", so I wouldn't exactly consider it a post, even though technically it does qualify as one.
At least the way that I read the question, they want to know if a stored procedure can return a result set as XML. This allows the web page to construct a generic page, then fill it with an XML result set without knowing/caring whether that XML came from SQL Server or another XML source.
Unfortunately, I felt like I was dancing around knife blades, since I answered the question as it was asked, but I could see a thousand shades of meaning that could have colored my answer.