After researching this product on the web, I found that Weld Aid is a chemical product sold in several forms. Mostly liquid for precleaning industrial metal products. Some cases it is used to coat tooling and fixtures to reduce weld splatter from adhering. There is also a version to preclean wire fed into Mig welders.
As to using this product in a resistance weld joint? You can try it of course.
I see not benefit and it would not be high on my list of experiments.
This is an extra operation/process step to apply something that may not add to the process. Additional chemicals in the joint may act as contaminants?
The spot weld process is going to melt and burn all surface contaminates away that this cleaner may remove. Don’t add another item that must burn off. If they don’t burn off, they could affect the weld joint.
DIRTY SCALEY MATERIAL
Don’t add another chemical byproduct into the mix.
If your input parts are extremely dirty, oily or oxidized there are precleaning methods to correct this, without adding another layer of chemicals to the mix.
"Weld Aid" preventing weld splatter adhering to tooling and fixtures may be worth investigating.
Reference: RWMA – Resistance Welding Manual 4th Edition