Gel polish is not an overlay, an overlay is a strengthening product such as Gel, acrylic or hybrid. Gel polish is a light cured polish. They are different products and require different training.
As for your question, check with your insurance company that they accept the training provider's qualification, not all providers are accepted.
Check with TGB that they accept the training providers certificate too.
Not all pro brands will accept all providers certificates. This is because there are lots of people offering substandard courses. They provide certificates of 'attendance' not 'qualification'. Attendance just means you attended, it doesn't necessarily mean you were competent on completion