So they're not so much "Santa's helpers" as "Santa's POWs."
I'm hearing little piping voices in my head, singing, "That's the sound of the men, workin' on the chain.... gang..." They planned an escape once, until they realized that if they left Santa they'd lose their only bass capable of carrying the "Well don't you know..." line.
It explains why the hammering is always so precisely rhythmic, at least...