I'm not a fan of Aluminum flex & where it is used doesn't change my opinion.
However, 348.12(1) allows flex to be used in wet locations with the proper type of conductors when the flex is installed so thatliquid is not likely to enter raceways or enclosures to which the conduit is attached.
In all likelyhood, the flex installation you describe contains an equipment grounding conductor, so the corrosion shouldn't be that much of a problem.
Around here, things can get quite competitive, but no one is so cheap that they have to save 20 cents a foot on the cost of sealtight & maybe $1 to $2 for the connectors.
Few things are harder to put up with than the annoyance of a good example.