Gabban can only appear if Vulpes Inculta has died before reaching Nipton, which can happen by skipping Nipton and then killing Vulpes on the New Vegas Strip when exiting The Tops after completing Ring-a-Ding-Ding!
Gabban's dialogue within Nipton is nearly identical to Vulpes Inculta's, differing only when Gabban refers to himself in addition to some minor punctuation changes. Also, he provides much more information about Caesar's Legion than Vulpes, he can be directly asked about Lanius, for example.
Gabban has the same face model that Dead Sea and Alexus have, but Dead Sea and Alexus do not appear unmasked in normal gameplay.
With the Terrifying Presence perk the player can tell Gabban "I'm going to wear your head like you wear that dog's.", referring to the vexillarius helmet worn by Vulpes Inculta. However, Gabban does not wear nor carry a vexillarius helmet.