Hi Mike,
VCSMC 5.5.1 is not under active development. So the notes are not updated (and mostly won't be).
VCS QA does some in-house testing to see if it is compatible with the latest versions. Since the product itself is not active, the testing is not taken to the level of "official qualification".
But QA does basic sanity with the product. There are users who are still using VCSMC, and so this testing is done to anticipate any questions that customers might ask.
According to that testing, it works with VCS 5.1. As discussed, VCSMC 5.5.1 works with VCS 6.0 non-secure clusters, but not with 6.0 secure ones.
Regards,
Amit.