Vented gas cap-- ok in garage that is under the house?

a vented cap will vent the gas fumes to the atmosphere (read, your garage/home)
a properly working canister will not "vent" at all
it will store the fumes in the canister untill you fire up the engine
then a valve operated valve will open and the fumes stored in the canister will get released into the PCV system, sucked into the engine and burned of

if it were my car, my home and my family, i would go through the trouble of reinstalling a canister
as a matter of fact, when it came to my car, that is exactly what i did

(this thread has partnumbers and pictures of my setup)

Vapor/Charcoal Cannister