Quote;
"When a manufacturer puts a cap on their valve stems, they use plastic, not aluminum – for a reason. Plastic caps on brass stems protects your wheels. Aluminum and brass is a recipe for disaster. When they overheat or become exposed to too much humidity, the aluminum and the brass oxidize. This causes the tire caps to fuse onto the tires."

...would this apply to our wheels??

Hmmm. I would argue the reason the mfr uses plastic is they are CHEEEEP.
Here are my thoughts:

The function of a valve stem cap is to:

1) Seal out exterior dirt and moisture from getting into the valve.

2) Prevent any air leakage from the tire should the valve leak.

3) Look good?

In my experience the plastic ones often do not have perfect threads and do not seal around the end of the valve. The metal caps I have used have much more precise threads and a rubber oring/gasket inside to provide a perfect seal for water, dirt and air. I have never had leaks with metal caps.
As for "when they overheat or become exposed to too much humidity... the caps fuse onto the tires." What?
If you get the valve stems that hot you've got way more problems than fused caps. Boiling brake fluid, bearing failures, blown tires, leaking stem valves, etc.
As for humidity, maybe grease the threads a bit? (You can get chrome or brass caps to avoid corrosion.)
Meanwhile, how long has it been since you checked the pressure in the tires if the stems are corroded???

I strongly recommend the metal caps with internal gasket.
They seal much more reliably. (I think they look better too.)
You can get them with the little prongs to remove stem valves. Plastic is junk.

Be nice to know the source of the quote as Steve is so right.

On my Chevy Tracker I did have two caps corrode , wouldn't come off had to replace stems. I figured they were made in China.

I could easily see the aluminum corroding and causing problems. For sure some antisieze or lube would be good on the threads. Aluminum caps would be my least favorite metal but still better than plastic.

I do prefer the old standard steel with stem remover end. I miss the plastic caps I got for my bicycle stems around 1950 that were the red Standard Gasoline Crowns, they had the gasket seal in the top.