John, the target org must have LWC support enabled. At present, this is limited to scratch orgs created Spring '19 pre-release orgs enabled as dev hubs and Spring '19 orgs that have been explicitly enabled by Salesforce support. I have only tested against the former. Here's Salesforce's documentation on getting started with LWC right now:
and for the most part, that applies equally for IC except for the dev tools portion where you'd just install the latest build of IC.
FYI, I developed/tested support for LWC against non-scratch orgs by creating a scratch org as described above, adding another user to the scratch org with a password and security token, and creating an IC connection as that user. Technically it was still against a scratch org, but using it as if it were a DE org or similar.
I hope that helps. Please let me know if you have any other questions.
Regards,
Scott