Regarding only being able to work with a morph in ZB in a single session. Poser appears to use the name of the sub tool to determine if its handled as a morph or obj when being imported back. If an older model is made to look like the subtool just generated by the Goz bridge, Poser can take it in as a morph. I don't know how reliable this process is but if a Goz session fails and you're faced with losing all your work its worth a try

Save the tool you're working on so there is a backup.
Start a new Poser session and load the base figure
Goz the base figure. In ZB there will now be a new tool for the base figure
Append the older tool into this to create a second subtool Rename the second subtool to match the name of the first
Highlight the older subtool and press Goz, it should go back to Poser as a morph