Ever since there's been pop music, there have been covers of pop tunes played by various classical ensembles and orchestra. Depending upon your point of view, Arthur Fiedler can generally be given the credit or blame for creating the modern version of this crossover category.
CSO conductor Albert-George Schram and I talked about this at some length in a feature we did a few years ago I called Fridays with George. He one of the most difficult things in the world to do is to get "a symphony orchestra to rock." Elsewhere in the conversation, he said it really comes down to the arrangement. Taking a pop tune and turning it into something palatable and engaging for an orchestra can be a tall order.
On the other hand, things have been going the other way for a long time. Tchaikovsky, Prokofiev, Chopin, Bach, Mussorgsky, Copland, and many others have spent more time on the pop charts than you might realize.
Here are a few examples:
Leos Janacek - Sinfonietta (with a little Bach for good measure) was used in Knife Edge on their first album.
https://www.youtube.com/watch?v=TQQdYokbp4E
Aaron Copland - Simple Gifts in The Greatest Man that Ever Lived by Weezer
https://www.youtube.com/watch?v=aPZCGleqh7M
Mika did something a bit less noticeable by using the main harmony from Rossini's Largo al factotum in Grace Kelly.
https://www.youtube.com/watch?v=0CGVgAYJyjk
Sting's 1985 Russians from his album Dream of the Blue Turtles used an arrangement of arrangement of the Romance in Lieutenant Kijé by Prokofiev to great effect.
https://www.youtube.com/watch?v=wHylQRVN2Qs
Now to the reason I mentioned Lady Gaga in the title. She borrowed an eight-second snippet from Bach's Well-Tempered Klavier for her 2009 hit Bad Romance. If you know anything about LG, you'll know her videos are, how shall I put this, a bit out there. She writes great, catchy tunes, but her videos sometimes make you rub your eyes and say, "Did I just see what I thought I saw?" There is a link above.
Italian composer Giovanni Dettori doesn't believe in lines of division in music. That is well evidenced by his Lady Gaga Fugue. Listen to it before you laugh. Bach goes pop, then goes back to Bach. Yes, that IS Michael Tilson Thomas conducting the San Francisco Symphony.
https://www.youtube.com/watch?t=121&v=XYFMgeBaLUQ
Mr. Dettori has done a Miley Cyrus Fugue, a Brittany Spears Counterpoint, even a fugue on Katy Perry's 2010 single Teenage Dream.
You can see them and more here.
Musical lines have been blurred for a long time. The walls will continue to crumble if Giovanni Dettori and his friends have anything to say about it.