McGregor wasn't on welfare - he was on jobseekers allowance (which was 188 euro per week at the time). This is why he named his yacht '188' - to remind himself of where he came from. Job seekers allowance in Ireland would be the equivalent to unemployment insurance in the United States.
After school he became an apprentice plumber and he left his apprenticeship in order to train in MMA. He was living with his girlfriend and she was working full-time and he was receiving jobseekers allowance (188 per week).
Technically he was breaking the rules as he wasn't actively seeking employment, however, he wasn't on welfare. What he did was no different from what construction workers do in the US - when the construction season slows down in wintertime they apply for unemployment insurance.
Seems like you're giving him a generous review of the situation... But I don't know Irish welfare laws. He calls it welfare here:
Conor McGregor collected a $235 welfare check one week before becoming a star in his first UFC fight
Conor McGregor could earn $100 million for his bout against Floyd Mayweather, a far cry from where he was just four years ago.