That is not realistic, emphasis on NOT! Tolerance is not what they would require in your neck of the woods - full blown resistance is what they would require - imperviousness would probably better - not many Agaves (if any) fit that bill.
Many Agaves take cold just fine, but only very few will take cold and wet for 6 months or longer at a time. A. parryi truncata will definitely croak if left wet and cold.
Ovatifolia - you might be OK - it is more of a high mountain species so does see cold and wet - but then again not 6 months in a row. I know they survive on the east coast where they get months of snow in a row, but I would still worry about just rain, rain and more rain.
So my advice: Move the plants under rain protection or move rain protection to them. If you have multiple plants of each you could experiment, but I would mentally prepare myself to loose the one exposed to the moisture.
Here in Arizona we have the opposite problem - which Agaves will take the full sun and >100F for months at a time - again you'd be surprised at how few actually pass that test, most still want some protection from that sun at least a good portion of the day, as several dried up husks in my front and back yard will attest.
