Its one thing to ask for a Bracha to be a success for a normal job (Like a teacher)
However gambling isnt a normal livelyhood
If you have ever been to a Racetrack or most casinos (Las Vegas does get a higher class of people) you will see the people who hang out are not exactly chashuv people
Wasnt there some story of the Chofetz Chaim being asked to bless a lottery ticket and he refusing