You could ask a different question and get the answer you require, IS TNA a threat? Well, nope, not yet and not for at least a good while will they be. And if TNA is currently not a threat, then there is no reason for WWE to view them as such. The example you gave isn't them being worried about the threat someone wearing a Hogan T-shirt may instill, it's just obvious that your not going to plug the competition to help them along, even if they aren't a threat to you right now, that's poor business smarts.
WWE won't be seeing TNA as a threat currently, but they aren't going to be doing them any favours unless you considered them plugging Mick Foleys book a free ad for TNA, but that's debatable. It may also be a little bit of what Kofi Orton said, a shot at Hogan because of what he did to devalue WWE's HOF, with his bismurching of the HOF ring he was given. Either way, you see TNA take shots at WWE often because they know they have to make a name for themselves challenging the big company. WWE doesn't take shots at TNA because they are the big company and they don't have to focus on anything else but themselves... ultimately because TNA isn't a threat. If it was a threat.. then just like during the monday night wars, you'd see WWE shooting over at TNA, but as this isn't happening, you know WWE's stance on TNA.