I have vers. 1.3 and have just double checked this. I can add Insert effects to the drum channel 10 and hear the changes as they are made. I can select the effect I want directly for ch10 when in the Song Channel of Mixer (Effect menu) , or I can use the Assign screen, making sure ch10 is first selected and although a little complicated it seems to work OK.
It is very similar to how you choose insert effects for styles or panel voices except you must select the appropriate song channel instead.
John