Online backups with VENDOR library: what should be set for ACTIVE LOG PATH?
The active log path (database configuration parameter LOGPATH) for a database MUST be a locally accessible directory on the database server.  Preferably one with very good read/write performance.  (I'd say it must be a local directory, but technically you can specify the path on an NFS mount).

When DB2 fills a transaction log file (and all transactions contained within have been committed), the DB2 log archiver process will copy the file according to what you've set in the LOGARCHMETH1 and LOGARCHMETH2 configuration parameters.