You have the process form (shown for example when your process execution starts) and human task forms. Currently the processid attribute you set in the process properties and the taskName attributes you set on tasks control the name of the forms that should exist either in your Guvnor repostiroy (if you are using Guvnor) or in your classpath. Those are not "attached" to your process definition (do not become part of the BPMN2) so in order to see if your process has a task form defined and/or if your human tasks have their task forms defined you would have to determine the file name first with the above mentioned rules, and then check either in your repository or on classpath if it exists or not.
If you generate your forms in Designer, yes, as you mentioned the form files will be created and uploaded into Guvnor for you.
HTH