A fellow board member and collector pointed out yet another card where the artist took the liberty to rotate the image (once again) about 20-25 degrees counterclockwise. Found at
T206resource.com, you can also see the same artistic tilt effect used on the Patsy Dougherty card.
Although the debate of horizontal vs. vertical might be getting a bit old, this discussion does give a little insight into how these cards were originally laid out and cropped by the artists who helped create what we call The Monster.
It seems like in each case (Bender, Dunn, and now Dougherty) the guy laying out the artwork on the card rotated the image about 20 degrees counterclockwise. In the case of the Dunn, it creates an odd effect if you view the card vertically, but with Bender and Dougherty it fits the card.
I can also see why the artist took these liberties -- he/she had a fairly narrow window to work within, so these changes were possibly made to make the player "fit" on the image space of the card, without having to show a bunch of dead space above the player.
In conclusion, I believe the original image used for the Dunn was a shot of him standing upright to make a basket catch. However, it
is possible that the intention of the artist was to give the viewer the effect that Dunn is diving -- it's
possible. 
Here's the Dougherty comparison, and what I think the Dunn card
would've looked like if the artist did not use the tilt effect (notice all the dead space I had to leave above Dunn, almost making it look like an E card)...