I dropped my validation report database and then BaseX was able to start as expected.
That’s unusual. No databases should be opened or initialized if you start basexhttp. The only files that are parsed are .basex and (optional, if they exist) data/users.xml and data/jobs.xml. Feel free to share more information with us if you can.
If I understand the docs around file locks and so on, it is safe to have databases shared between servers for read and as long as writes are done from the data processing server the page-serving server should be good.
Yes, if you know exactly what you’ll be doing, it’s feasible to let multiple BaseX instances run on the same database folder. As long as you don’t access databases that you create, update or delete via another instance, you should be fine.