No it isn't barebacking as there is no penetration. Penetration makes a huge difference with risk factors. Even the activity in the GIF is considered low risk for most STIs apart from skin to skin transmission eg HPV and HSV and as I said earlier probably on a par overall with OWO.
Me too, the risk is unintentional penetration, it's quite easily done. If I could be arsed I'd find the review of a masseuse who did that while doing B2B and the punter nearly went in. He pointed out the risks and she stopped doing it. As any sensible person would.
What's the risk of catching something through unprotected penetration, 
Whether you mean it or not it's still penetration.
You're both right.
Doc is correct that hotdogging in itself is relatively low risk.
dm is right in that if you're not careful during say FBSM, where the WG is sliding around on top, if the correct angle suddenly occurs (and perhaps an unintended movement from the punter), suddenly there can be unintended, momentary penetration.
Not to mention in the heat of the moment, instinct can take over for a split second and in it goes.
Both the above happen with the gf (or even wife if you're still 'active') but it's all teasing fun and doesn't matter, it's just a matter of when, not if. Of course with a WG though, a completely different ball game.
As has been pointed out though, strictly speaking hotdogging is sandwiching the cock between arse-cheeks (not cameltoe), and doing that the risk of unintended penetration then is obviously minimal.
