SeoTools is written in C# and does not contain any VBA code. It is possible to use the Seotools formulas within VBA, here are some examples:
I have personally worked a lot with VBA and it does some web-scraping but the language does not have the same power as .Net and other alternatives. The benefit is that you get better control over the worksheet and can write ad-hoc solutions quickly.
SeoTools itself is not open-source, but you are more than welcome to write custom connectors. We host them here and copy-pasting will get you a long way. With a bit of training, you can write scrapers very quickly.
Here is a non-finnished guide of Connector-building.