One of the selling point of Jayco's is the Magnum Truss Roof system, which is built stronger than most travel trailers. They are supposed to be able to hold up to 4500 lbs across the whole of the roof. I'm not sure if the SLX line (formerly the JaySwift I believe) has that same roof construction. On the Jayco website, it is a selling point of the JayFlight and Eagle lines. The SLX line doesn't mention roof construction.
Contact your dealer, or better yet JAYCO and ask them. For that matter, my trailer is a flat roof with 2x2 construction, no ladder and no mention of "walkable roof". I have installed 2 roof vents and crawled across my trailer roof both time to install them. I stayed low and spread my body weight out, rather than all the weight on a single foot at any time.