I'm going to guess that the answer is yes. Especially if the beer has been in there for a while. Best advice: Replace the line. It's only a few bucks, band would be a good piece if mind.
I'm on the yes bus too. CO2 does nothing in the killing/preventing department. If the bacteria has a comfy place to live and something to eat it will thrive.
Not sure about this one since bacteria typically function through aerobic respiration. I'd still want to thoroughly clean or replace the line to be sanitary about it.