When you try to view a object which contains a collection in OME, you cannot descend into the collection-items. Instead you see only the collection-type.
To descend into the collection-members, OME needs the original classes. Therefore you need to specify where the assembly for this class is.
Go to "Tools" -> "Object Manager Enterprise" -> "Options" menu and select "Assembly Search Path...". Add the path to the assembly, containing the type definition. Now disconnect and reconnect the database and browse the objects again:
After that, the collections-members a visible.