Hah, funny you should mention that...
Yes, signmaking vinyl works great! I have been in the business about 7yrs now. I thought I was a genius, applying my graphics business to photoetch and dispensing with all the "photo" hassle of it. But the sheer tedium of weeding (picking out) all those little pieces means it's only easier if you're making one or two for yourself. So I trashed the idea, but it's quite feasible for the do-it-yourselfer.
You know, as the brass etches, it etches in all directions at once. The process of etching "sideways" underneath the resist or vinyl is called undercutting. Thin material undercuts very little. Thicker will undercut much more, which requires that you put identical art on both sides so the holes will meet in the middle. For that, getting near perfect alignment is a must, and is a real hassle with computer cut vinyl. Plus you don't know if it's wrong until you ruin the brass and waste your time. But for thin material, it sounds like you could do a million little one-time projects.
When you set up your file, plan on the acid eating up 20% extra of the material thickness. If your relative's plotter has a swivel knife that casters behind the carriage (most do) then the square corners where the knife turns may have little boogers that can make trouble. There is a setting on the plotters to correct this called "corner sharpness".
Also I have an idea for ladders on a nautilus type boat. You would etch thicker brass into a ladder shape, purposefully too fat, then peel off the vinyl and dunk it in the acid for a while more. That will round off the lines and you can bend the four ends 90 degrees, all the same direction. It would make a standoff ladder that had a very delicate rounded look and no solder to clean up at every joint. Just an idea.