Generally... fret buzz is caused by a fret that is in the eliptical pattern of the string vibration... Light strings tuned to standard will have a wider vibration pattern than heavy strings tuned to standard... BUT, the heavier strings are also obviously thicker... which may cause fret buzz either way... So, in short... no... Thicker strings don't always mean lower action with less fret buzz...

Certain guitars are designed to operate more like acoustics... where neck relief is used to reduce fret buzz and supply ample action... Some guitars are designed to not have a specific area of operation as far as action is concerned... I've found that the best guitars for low action are hard tail bridged guitars with compensated necks... i.e. Gibson LP's and Schecter C-1 series guitars... The lowest AND cleanest action I've ever seen on a guitar was on a Schecter C-1 Classic Diamond Series with a set of .9's on it... So it depends on the guitar as well.