I've now gone through all the questions that have SAML (third party SAML in particular) mentioned on this forum and I'm surprised to note that none of them have any answers. Is it 'cause third party SAML is not "really" supported (although mentioned in the documentation) or is it that 'cause VMWare has its own SAML implementation and couldn't care less for third party ones? Assuming the latter (in that VMWare couldn't care less), why not address the 404 error on that published ACS in the metadata? Does it really exist?
After close to 2 years away from this problem, I had to revisit due to customer request.
For anyone going through this and having similar issue, you will need to use a browser when RDP'd to the Horizon 7 Connection Server VM; I was previously doing it from my local browser when getting this error.