Keepass2 works well on Linux systems. You can use it directly with the WebDAV URL or with the keepass db file in your Seafile synchronized folder.
I changed to KeepassX recently because it does not depend on mono. It works very well, too. But I noticed, that opening the Keepass file with KeepassX leads to creating a hidden temporary file which Seafile then sychronizes and deletes it after the database was closed. This was a bit annoying so I made a seafile-ignore.txt to exclude the temporary file from syncing. You can look how to to that here: https://www.seafile.com/en/help/ignore/