UBA isn't a Splunk Enterprise instance, but it does include a Splunk Universal Forwarder (UF) as part of its install (see Directories created or modified on the disk section of docs).
So, you should have a UF living at /opt/splunk for your UBA instance, and that's what you'll want to make sure is hooked up to the rest of your Splunk deployment. Also note the Splunk platform port requirements section on that page for more info about that UF instance running alongside the UBA install.
