When Herb, Lisa and Bart are watching the Itchy and Scratcy Episode, Herb is wearing a polo shirt and shorts. When they roll about laughing, he is wearing shirt and trousers.
When Herb, Bart and Lisa are watching Itchy & Scratchy, Scratchy is turned into a milkshake, but in the next shot, he is seen onscreen fully intact.
Herb Simpson is obviously quite brilliant and successful, ergo he hasn't been affected by the Simpsons gene from Lisa the Simpson (1998)(#9.17). However, he does make several blunders, such as picking Homer to design the car without having any idea of his ability to do so, not supervising the development of the design and dismissing the design team's concerns over Homer's ideas, which could count as being affected by the gene to some extent.