Before the Series
In a flashback, he appears with Dr. Montgomery. They eat together and laugh together. The fact that they are in the V.F.D. headquarters confirm that they both are from V.F.D.
The Reptile Room: Part One
He sells tickets to everyone. He gives Montgomery a Verified Film Discount. Later, Montgomery needs him to play a part of the film again. He says that he sells '"multiple tickets", meaning he could be Captain J. S., mentioned in the Autobiography. 
In the TV series, he splices footage from Zombies in the Snow so that Montgomery can copy down the rest of the message.
The Carnivorous Carnival: Part One
In "The Carnivorous Carnival: Part One," the Ticket Seller is visible in a flashback attending the party at V.F.D. Headquarters with Montgomery when they are briefly visited by Larry the Waiter and then filmed by a camera operator. The Seller appears to be slightly puzzled at the note in the dessert Montgomery takes, though this may have only been to disguise the note's existence.