In my experience..YES! although it depends on your salt water conditions...If you are launching into surf or changing tides then you are not going to make it in anything over 1 ft. surf. If you are just asking if it will function with that boat type and in salt water... You have no problem mate! I however advise that you wash all gear off (including your minn kota) with fresh water after any significant use.Can a minn kota all terrain 65 lb thrust handle a 20' boat in salt water?
often, its less about the length or even the weight of the boat, and more about freeboard.
If you have a lot of hull out of the water, the wind will find it easier to manhandle your boat and you'll need more than 65lbs thrust to keep it under control in a stiff wind.
Calm day, should be fine.