While in Play mode, it seems to me that the only way to scroll the track vertically is by swiping on the leftmost part of the track area.
This means that you have to always move the pointer there while you are editing, each time you want to switch, say, from Flute to Violin, and back.
I would find more handy to be able to simply grab the page, and move it up and down. Or use a modifier key to swipe up and down. Here are the two alternative methods:
a) Click/tap on an empty part of the pianoroll, without touching any note, and hold it. Swipe up or down to scroll the tracks.
b) Keep the Command key pressed, and scroll the trackpad/mouse up or down.
The same can work for horizontal scrolling.