@nk271 - Based on what little I know, and my interpretations of your question(s), here's one option:
On Site A, implement impression tracking for the CTAs in question. Add a listVar to all page loads that tracks any CTAs that present on the page. (I'd capture the ICID values in the listVar.) Throw in a success event to keep track of impression counts (or just use the page views metric), and you should be good to go.
Since you're having to compare data across report suites, it would be best to keep the data consistent. This is why I suggest capturing the ICID value in the listVar. This should make for a simple lookup across the two data sets.
On Site B, you're already capturing the ICID so keep doing what you're doing. (No changes there.)
There may be better ways (like capturing the data for both sites in a single report suite), but this is one approach that should work without adding calls to Adobe. (You're just adding a property to the existing calls.)