I can fully see the insurance company's perspective - professional poker player probably means travelling up and down the country at all hours leaving your car unattended in some dodgy car park whilst carry larges amounts of cash. This all adds up to a lot more risk than an old retired geezer driving to his allotment on a sunday morning.
Or you spend all your time playing online, don't do as many miles in your car (as you don't have to commute). When you do play live, the car is parked in a secure car park with CCTV and security.
If you misrepresent your occupation then you are just asking for trouble, imagine you are a well know who gets his brand new M5 nicked from the Casino car park 200 miles from home. I would be certain that the insurance company ask more than the odd question and decline your claim.
What happens if my car gets nicked from a casino car park 200 miles from my home? If it was parked at a church and stolen - would that make me a priest?