"Cheating" is a matter of perspective. If you mean to do them that way, it might not be cheating. From a mechanical point of view, the more bent your arm is, the "easier" the rep will be since you're altering your leverage.
You don't want your arms locked straight because that'll direct the stress right to the elbow. But if you have them bent near-90 degrees, you've improved your leverage so much that heavier weights are possible, at the expense of direct muscular stress.
I agree that the slight arm bend shown is what the OP should mimic, but not the significant body swing... unless he's the size of Branch and using similar weight dumbbells.