I've read on here that it's not unusual for urine to not have an odor but I mean, if someone smells it and it's odorless..is that an immediate red flag? Can they fail based on lack of odor?
Nope. An absence of odor can occur in human samples as well as synthetic.

The red flags are raised when a collector catches wind of any unusual odor thats not supposed to be present in human urine (ie; bleach, household chemicals, gasoline, etc.)

Other than that, the collectors are not gonna arbitarily take a sniff of every urine sample. Thats disgusting.