I flew sailplanes too and towed them. It helps you learn unpowered flight and energy management but doesn't help much in an airliner. Sully flew sailplanes too but it had little to do with his successful Hudson landing.
Are you sure? I had always understood that his choice to ditch in the Hudson, rather than aim for a tantalisingly close airport was the critical point in the emergency.
So Sully quickly came up with a good overall
strategy [ditch]. Which both pilots then executed admirably.
IMHO a willingness to consider [perhaps even to recognise] alternate landing sites is a necessary part of glider flying. So Sully's background could have influenced him here.
AFAIR experiments on the simulator confirmed the importance of the strategy. Attempts at landing at the airport were mostly unsuccessful -- especially at the first attempt!