A substrate tray has a solid bottom, so nothing would drain into the drainage tray. You could put holes into the drainage tray, but if they fit it seems redundant. Are you going bioactive? That is one way to get the humidity up. Another is to add more live plants &/or cover the sides (3 out of 4) with plastic - either sheeting or panels. You can also run a humidifier in the room.
What kind of set-up do you have & #'s are you getting? Temps (and how measured), lights, humidity (and how measured).