I have, but the best example I can think of is a cousin of mine who has done it for many years. The 30-06 Sako that he carries this way have probably taken around 5000 animals. I have never seen this rifle with a sling The rifle wears a Lynx LX2 which is probably about the same quality as a Leupold VX2 I guess.
I think there is no problem carrying it this way as long as you have a decent quality scope and rings.