Right, I mean not mandatory. The Forms Training assumes you have a basic understanding of AEM -- the concept of Author and Publish, the role of an Author versus a Developer, etc. -- but the rest (including client libs, OSGi bundles) are introduced during the workshop. If you need a deeper understanding (which you probably will) then you will need to revisit AEM training but people should be able to complete the training successfully.
Having an understanding of the AEM topics you outlined in your original question -- templates, components, OSGi, etc. -- are a nice to have for Forms Training; At a minimum, you can take the FormsTraining with an understanding of the following: