Hi Jon,
As I understand it the component ZTL is more like a Java language implementation. However, in addition to this, you can also call any of the BIAL script APIs within a ZTL method as described in the Binding Events to Design Studio Script Methods section of What's Coming in Design Studio 1.4 SDK.
I'm not sure if you can create shared java libraries and suspect that .js libraries referenced in the <jsinclude> tags of the contribution.xml file are probably not accessible from ZTL methods, although I haven't tried this myself.
To get an idea about how to dynamically reference components you can refer to the source code of Design Studio SDK: Component Manager by Karol Kalisz.
Regards,
Mustafa.