How do cases like this work? If he is unemployed and has no income, can they still garnish wages and enforce judgement once he secures employment even to the point where the defendant may not be able to afford adequate housing to maintain employment, thus creating a cycle of non-payment?

In the US, this depends a bit on which state you live in.

For wage garnishment usually it is the LESSOR of 25% of disposable income (income after taxes and involuntary deductions) OR the amount that your income exceeded 30 times federal minimum wage (currently $217.50/week).

Nintendo could still go after other assets (bank accounts, property, etc) and the defendant can also declare bankruptcy.