The parse() function in dateutil can't handle time zones. The thing I've been using is the %Z formatter and the time.strptime() function. I have no idea how it deals with the ambiguity in time zones, but it seems to tell the difference between CDT and CST, which is all I needed.
Background: I store backup images in directories whose names are timestamps using local time, since I don't have GMT clocks handy at home. So I use time.strptime(d, r"%Y-%m-%dT%H:%M:%S_%Z") to parse the directory names back into an actual time for age analysis.