A UX position in the games industry is extremely rare.
The latter is where you can make the biggest difference, getting a decent research and test plan in place.
So before any design or development starts, conduct ethnographic studies, which is a fancy term for observing in the natural environment. Find out who your target audience is and how/where they game.. then go and watch them. You'll learn not only about how gambling games are played, but also a great deal about the people who play them and how they fit into their lives.
That will give you the base knowledge needed to be a 'user advocate in meetings'. It is also useful to write them up into some very brief personas of the types of players you are designing for, and stick them up on the wall somewhere as a permanent reminder to everyone. If you can record sessions and circulate, again that's really valuable.
Then, as the project progresses, test early and often.
Testing in games is generally done towards the end, and is split between bug testing and really rudimentary play testing - hiring any old person who happens to be available, getting them to play a game with no particular goal in mind, and then give them a questionnaire afterwards.
Instead, take it up a notch towards where it is in other industries. First, start with a clear goal for a particular test, the narrow a focus it has the more useful results you'll get. Next, if you've done the research as above you'll know exactly who your target audience groups are, so you can recruit the specifically (market research companies are a fantastic resource, but don't use them for research, instead pay them to do your recruitment for you) and then don't give them questionnaires, instead, simply watch them play. Prompt them for more information on what is going through their head by all means, but base that on watching their facial expressions and in-game actions.
There's a fantastic list of UX in gaming articles here, although you may need to be a member of the games user research group on linked in to be able to access it:
Here's an example of one of the articles from the list:
Something else that is a subset of UX and is also rare in the games industry, is thinking about accessibility. The negative and positive implications of accessibility for disabled gamers are both greater than web, especially in a sector as cut-throat as online gambling - it is still possible for your game can be the only game of that type accessible to a certain audience, in which case you stand to gain some hugely loyal advocates (with the blind audience in particular).
More information on accessibility in games is available here, even if the company has a resistance to thinking about people with disabilites (they sometimes do, through pure misconception and lack of awareness of business cases) it's still worth taking a look through anyway, as so much of it is just good general game design that benefits all players, the 'basic' level guidelines especially: