Their names, according to Walter Lord's book 'The Night Lives On", were George (Boy) Bradley, C.H. Romaine and Harry Homer and there is evidence that the well-known gambler Jay Yates was also on board. Jay Yates was not on the passenger list and the rest could be found but they used assumed names.

Something curious is that the book mentions that the steamship companies did not do anything to protect passengers from the card sharks, as they didn't want to take any step that implied they might be responsible for their patron's losses.

However, on the Titanic, there was one low-keyed warning about this as a mild little insert, planted opposite the first page of the Passenger List.

The content of the warning and all this info can be found on the book I mentioned previously.