If you send a player out on loan to a none playable league just click on the player, Go to attributes and at the bottom it tells you how many games hes played, I have Scotland as a non playable league but Celtic as a feeder club and when i send players out on loan to them the players are getting 30+ games a season, Same when i send players to Germany, Russia or Holland which are all non playable leagues i my save.
While i dont like sending players to non playable leagues i would rather send a German regen to Germany where he wont have a language barrier so will perform better than send him to the Championship for example which is a playable league for me but the player might have a language barrier and thus get less game time than he will in Germany, When it comes to Russians i find Russians clubs are the only ones who are interested in loaning them due to work permits i think so i try to avoid even signing those but sometimes the regen is worth a punt.
You cant interact with non playable leagues but that doesnt mean the league isnt being played and players arent playing games, While it is better to send players to a playable league i will use non playable leagues if the club interested have better staff, Facilities and just a general better quality of opponents, For example i would loan to Italy even if its non playable over League one or a poor Championship side with poor facilities and staff, But i always have the top leagues loaded as playable just so when i do loan out players the have the best chance of developing.