That is an excellent question, and HQ addressed that as point #1 under the rollcage portion of the safety rules:
3.E ROLLCAGE REGULATIONS
3.E.1 General Rollbar and Structure. Professionally-made full rollcage required.
While the official rules COULD I suppose go into everything that defines what a quality weld is, the simple statement that it be "professionally-made" covers those aspects.
The organizers embrace brevity of description to keep the rules more manageable and less daunting and admittedly require quite a bit of "common sense" that (in teacher speak) is sorta like teaching to the middle. They lose some people at both ends of the spectrum, and while it is neither Keto-friendly nor Gluten-heavy, their buffet will feed the people who voluntarily walk through their doors and want to give it a try either because of the advertising they've put out there, or the smell wafting from their general location.
There are lots of resources out there on the internet that will help to define what a quality weld is and looks like. If you are unsure, you should seek out a professional's help. Inherent in the term "professionally-made" is certainly the understood designation of "certified welder".
The best advice is to both head to a local Lemons event as a spectator and show up on Friday during tech hours and watch the inspectors look over the cars as they come through and ask questions during down time, and/or reach out to Lemons HQ and ask where you might be able to bring your car local to you for an UNOFFICIAL "pre-inspection" (emphasis on un-official because just because a car has passed an inspection once doesn't mean it will pass the next time it rolls through tech at another race).
A LOT of what goes on at tech is akin to Jacobellis v. Ohio, 378 U.S. 184 (1964)