Purely anecdotal, but yesterday friends and I made five separate connections between Island Line and the steam line at Smallbrook, with no problems other than Island Line services running about ten minutes late in the afternoon.
It was quite possible to turn up at Smallbrook and buy an IoWSR ticket on the spot with no pre-booking, although of course that's always dependent on their trains not being full.
Regarding access to the footpath, the photos attached show how awkward that would be. The stream and path beyond are just about visible in the zoomed-in view, above the left end of the sign. Apart from the juice rail, the rusty barbed wire topping the fence, and the amount of undergrowth to get through, would deter any such attempt.