I'm not sure whether to post this as an answer, as it is primarily speculation, but it seems likely that if someone really wanted to stop a Patronus, they could. If one were in a location protected by the Fidelius charm and the sender had not had the secret revealed to them, then they would not know where to send the Patronus charm.
In fact, the sender simply being ignorant of one's location, without any magic blocking that knowledge, is likely sufficient. It's not hard to imagine that Kingsley knew that there would be a lot of OotP members at the wedding, and that he specifically sent it there, rather than his Patronus finding them on its own. Snape sent his Patronus to Harry only after learning his location:
Carefully examining the text shows that Hermione had her beaded bag open when she told Harry where they had stopped. Phineas Nigellus's portrait inside it overheard Hermione and reported that to Snape. Snape thus knows that Harry and Hermione are in the Forest of Dean
Muggles' Guide to Harry Potter, Harry Potter and the Deathly Hallows, The Silver Doe - Greater Picture
There isn't much reason specifically to think that warding charms keep Patronuses out, but there's not much reason to think they don't, either. Believing that they don't would require believing in some special exception for which no evidence is given.
The Patronus just appeared in the middle of the wedding without any invitation.
The Patronus itself may not have had an invitation, but it's reasonable to think that Kingsley had an invitation.