Zinc seems to be unable to handle struct types correctly or like vJass. I have two libraries and each of them declares a specific struct. library A requires library B and B doesn't require A and there is now library cycle requirement error. However, the struct declaration of library A is copied into file "currentmapscript.j" before library B's one and it doesn't know how to treat the struct name.
Actually you should be able to use struct methods from everywhere since they will be evaluated or executed automatically?!
Didn't enable anything in jasshelper.conf.
edit: If you have a Zinc library and you call <structname>.init() from function called init JassHelper assumes you want to call init with library prefix as a method of struct <structname>.
edit2: Seems that Zinc can't treat identifiers correctly. There are several problems with functions and structs in libraries, too when using Zinc instead of vJass.