On a related note, I've been watching an anime where a hymn is recited. After searching it I cam across only one mention on Google: http://the-free-lands.wikia.com/wiki/The_Corpse_Song_(Hymn)
The page states that it is "a partly translated hymn discovered in several ancient Tof temples engraved into the walls of what are believed to be either sacrificial or altar chambers." Would anyone be able to validate this statement? It may very well be entirely made up, so no need to search too hard. ;)
The page you link to is completely fictional of course, but the answer to your question about historical examples will depend on what exactly you mean by "hymn". Do you mean any kind of verse text? Or do you mean specifically a song designed to honour a divinity?
If the former, then the world is filled with millions of graves that have verse epitaphs. In my own field, ancient Greece, somewhere over 3000 verse epitaphs survive. Here's a particularly famous one, associated with the battle of Thermopylai:
O stranger, announce to the Lakedaimonians that here
we lie in obedience to their decrees.
I'm not about to give an encyclopaedic survey of the entire world's history of verse epitaphs, so I think it's reasonable to ask what kind of background info you're looking for. If it's just something very general that you're after, then maybe you could try something like Petrucci's very abbreviated book Writing the Dead: Death and Writing Strategies in the Western Tradition (Stanford, 1998) -- though it's not actually a good book (far too general, too telescoped, contains errors) so this isn't really a recommendation as such.