So a quick answer is no, you cannot use Related Records field to pull data from a Table field (i.e., Sub-Table) from another App using native features.
Native Kintone Plug-ins Method - Yup
Table Lookup Ver. 2.7.0 Native Kintone Plug-in allows Lookup fields to map row values of a Table (i.e., Sub-table) in the Lookup field's source app, to a table in the current app.
It is free for Kintone.com Subdomain and is supported by the US Team.
Using Get Records & Update Records API, you can build out a button to grab any fields from App A or App B and display it somewhere in your Subdomain (not limited to a specific App, could be in the Space Header).