Hello jbgorrie
Welcome to communities.
Skyline Advisor is a cloud based application which connects with the Skyline Collector to collect any logs. There is no manual option to upload the dump from a host and the logs from the host are collected using vCenter. As you would already be aware that Skyline Collector utilizes vCenter to communicate with ESXi host.
Runecast does have an off-line version which is installed on-prem and doesn't require external network, However with the help of runecast you would not be able to utilize the advanced feature which are provided by Skyline (Advanced Findings, Upgrade Assist, LogAssist, Few additional feature for Prem customers)
Do let us know if you want us to share any documents which would be helpful for you to clarify the question and receive approval.
Sincerely,
Triveni Shanwad
Skyline Support Moderator