SGC studio set, one of the last times it was used before being dismantled

Good question. I would guess that shallow might be opposite of long in this context. The term money pit is usually referring to wasting money, but I'm not sure how it relates here.

This is a quote from Joseph Mallozzi's blog that references it, but doesn't solve the mystery:
"Shallow Money Pit Hallway? It was used for the crucial Icarus Base evacuation/corridor cave-in/explosion sequence in the Stargate: Universe opener. Back in the day, we used to see a lot of that Long Tall Hallway – for instance, the scene in Window of Opportunity where Teal’c keeps getting hit by the door."

edit: JM calls the long hallway "tall", maybe shallow is referring to the low ceiling height of the Shallow Money Pit.