Hi, thank you for your forum post.
Unfortunately it is not possible to create a single project that supports the adding schema's of different databases.
You can at Step 5 of the project creation process, add another schema from the same database, but you cannot add a schema from a different database.
If you would like to see this added to a future version of the product, please post your suggestion in the Oracle Tools User Voice FORUM.
This forum is actively monitored by the Product Managers and Development Team. The more votes your suggestion receives, will increase its chances of being included in a future version of the product.