I would like to know if it’s possible to:
Access to Redmine through Zammad.
Link ticket from Zammad to Redmine
Sync states between them
See current state of the linked Redmine ticket in Zammad and vice versa
Sorry but as least from Zammad side what you’re trying to achieve is currently not possible at all.
You can use link template objects to add a link to the redmine issue, but that’s about it I’m afraid.
Can’t talk for reminde of course. Easiest way to get ticket information technically for a system would be Zammads API.