(Unique game aspects not part of story canon)
The Degeneration Merchant is an entirely different character from the Resident Evil 4 Merchant. He doesn't say as much as the Merchant from Resident Evil 4 and sports military attire similar to some of the special force soldiers in the game. He wears a gas mask of sorts however.
The RE4 system returned in Degeneration, though is much simpler. Resident Evil 4: Mobile Edition has another "merchant" version whereby the player is taken to a pre-game lobby where they can sell and upgrade items; it is therefore more comparable with the Resident Evil 5 system.