UK
Here in the UK, benefits come from general taxation. Until recently, fraud was accepted as a problem, but not too much was really done about actively looking for it. Now, the government are taking a harder line with benefit fraud, and even offer rewards if someone is prepared to "grass up" a neighbour, friend (or enemy!), work colleague. This is indeed happening with injury insurance, as citizens are paying directly through much higher premiums.
In this case of poker winnings, I believe the situation is not as simple as it seems. While gambling winnings are not counted, either for benefit or tax purposes, there is an exception, and that is where the gambling is the MAIN source of income for the person, and is worked at as though it were a profession. This may well apply to a poker player who is able to consistently turn a profit long term. It will be considered as self employment. The problem for the benefits and tax agencies is that the income would be irregular, and cannot be relied upon. This would make it hard to assess, and it is likely that they will require a change from Jobseeker's allowance to income support, where any net income over the long term will be deducted from future benefits.
There are indeed similar rules for Incapacity benefit, which limit the amount of income that can be earned from casual employment, and further restrictions apply to what work can be done, and permission has to be obtained even for unpaid voluntary work!
Any UK player who can consistently turn a profit long term from poker should try to obtain a ruling from the benefits helpline. It should be possible to obtain general advice without leaving your name.
Perhaps the Gutshot club would like to sponsor your case
, as they lost theirs as the jury did not believe poker was chiefly skill. If the benefits agency rule that poker is a "income generating profession", and cut back benefits, this would allow an appeal to have poker classed in the same league as Darts or Snooker, and the Gutshot would be back in business.
I hope KK declares his regular profits