Remote User Sync - Question

I would like to use two sites: one having fluent community and the other having directorist. I hope to use remote user synch to connect the two sites so that users can have access to both sites seamlessly.

The question I have is, if I am using fluentcrm, do I need to have fluentcrm on both sites or can I have it on the main site (fluentcommunity) and then have it connect to the secondary site (directorist)?

Any advice welcome!