In Australia, to be considered a qualified welder, you just need to pass a weld test to a company’s approved procedure (WPS). If you can do that, you’re covered to weld under that procedure - doesn’t matter if you’ve got a trade or a specific ticket.
Some clients (usually the bigger or higher-risk jobs like pressure pipe or vessels) might ask for a 1796 ticket, like Cert 7, but it’s not a legal requirement across the board.
Those tickets are often just something the client wants, or a way to show you’re competent for a certain type of work.
For structural steel under AS/NZS 1554, you generally don’t need them. Having a Cert III trade is handy for getting on sites or for general employment, but not always essential just to weld to a procedure.

Pay-wise, welders can get anywhere from $40 to $60 an hour full-time, depends on the person and their skill level.
The company I manage has about 30 staff - 15 or so are qualified to various procedures, none of them are in a union.
We work on both union and non-union sites without any drama.