The manual states that in this case you won't be able to use a horizontal menu and can't export pdf's. Or is there a workaround ?
That's not completly true. It's recommended to start Aware IM using startAwareIM.sh (giving you the Control Panel) when publishing your Business Space. Once published you can also use startAwareIMNoGUI.sh. But you still need to have for example GDM running waiting for graphical logins.
In case you don't have a graphics card on that machine there is (at least in Ubuntu) a fake driver that should allow remote X11 sessions. But I have to take a closer look at this.
Since build 966 there is a headless=true option that allows creating pdf files without a grpahical environment.
Again, this is not completly true. You need a graphical environment when you publish your Business Space. But after that you don't need any graphical stuff at all on the machine.