RE: Does this work on a basic WordPress.com site
Doubtful since the permitted plugins for the basic is very limited. Looking at the docs, it seems you would need a WordPress.com Business account.
RE: Can this allow more than one directory listing to be compared to other directory listings in a search?
Do you mean put separate directories on different pages? If so yes, by separating them by category. Here’s a FAQ for cMap which explains how. The same would work for Slim Plus.
Hope that helps!