Difficulty, Act or the Npc you choose to gamble with, have no incidence whatsoever in the odds of obtaining a better item through gambling.
Note that the quality of items is determined entirely by the Character Level that is gambling.Gambling can only be influenced by certain items, like for example Gheed's Fortune, that lowers the price demanded by Merchants but does not have a direct impact on the odds of getting a better item. Instead, the odds are affected by your character's level. Difficulty, or whom do you gamble with, does not affect the odds at all.
