Could work, yes. It might be a bit too much information though. When having the complete information, the player will be able to prepare everything before the drop and it might not be so enjoyable (there would be no surprise, nothing to react to).
I was personally thinking about some indicator on top of the screen where exactly something will enter the screen. It would appear only a few moments before the minions drop. Then you’ll do some playtesting and if it is still not enough, you can play with the timing, or even add different indicators for various minions.
I was trying to find some examples. There are several games (side scrollers or similar genres) that utilize something like this. It is there to prepare the player to react to something that will enter the scene momentarily. The only example I could find from the top of my head was Jetpack Joyride:
There are exclamation marks in the locations where a projectile is about to enter the scene.